Document 1129385

UNIVERSITAT AUTONOMA DE BARCELONA
FACULTAD DE CIENCIAS
PHD THESIS
by the Universitat Autonoma de Barelona
Speialty :
Astrophysis
Some observational and
theoretial aspets of osmi-ray
diusion
Defended by
Elsa de Cea del Pozo
Thesis Advisor: Diego F.
Torres
prepared at Institut de Cienies de l'Espai,
defended on July 2011
IEEC - CSIC
To those who believed in me, despite myself.
iii
Aknowledgments
Esta tesis nuna habría sido posible sin mi jefe. Diego me ha abierto las puertas al
mundo de la investigaión, enseñándome el ompromiso que implia, tanto a nivel
personal omo profesional. Por su dediaión y esfuerzo, por aompañarme durante
mis primeros pasos en la dura arrera ientía, quiero darle las graias. No sólo
me ha aportado su experienia y onoimientos ientíos, sino que también me
ha brindado la oportunidad de trabajar on estupendos olaboradores, de los que
espero seguir aprendiendo en el futuro.
I want to aknowledge my great group-mates: those who are, and those who
were. They have helped me through the hardest parts, being patient many many
times, and always trying to teah me something. They even onsent to go with me
outside the working world, and shared a few laughs! Agni, Ana Y.: I miss you girls,
thanks for putting up with me in my lueless rst years. Nanda, Andrea, Ana and
Gio: I have nothing but smiles and huge thanks to you all, I'll see you on the road,
I'm sure. Also, I sent my gratitude to those whom I have the pleasure to work with
and that have taught me a great deal of useful things: Stefano and Olaf, thanks a
lot.
I have met wonderful people inside the MAGIC Collaboration, and I would like
to thank them, too.
Working with you has been a really interesting experiene.
Moreover, I had a really nie time with many of you outside the work, both in La
Palma and in any ity we had a meeting or a shool. I hope to be in lose ontat
in the future, no matter where I end up being.
I almost wish I hadn't
gone down that rabbit-hole
and yet and yet it's rather urious, you know,
this sort of life!
Lewis Carroll,
Alie's Adventures in Wonderland
He tenido la suerte de onoer a gente estupenda en estos uatro años en
Barelona. Sin ellos, mi vida aquí habría sido insoportable, y es a ellos a los que
más eharé de menos uando me haya ido. Siempre había pensado que onseguiría
esribir algo espeial para ada uno de ellos, pero dado que soy un poo desastre
y que, bueno, no me estoy muriendo, sólo me voy un poo más lejos, pues tendrán
que onformarse on lo que hay.
Empezaré por mis ompis en desdihas: los iberianos. Esa extraña poblaión
de estudiantes apaz de trabajar en un lugar sin puertas ni ventanas, y aún así
reír y animarse mutuamente.
Por orden alfabétio: Ane, Antonio, Carlos, Dani,
Diego, Felipe, Jaobo, Jonatan, Jorge(s), Jose, Juan Carlos, Nataly, Pris, Santi. Ser
iberiano se lleva en el orazón, reordadlo.
Y si me he dejado a alguien, no me
iv
peguéis muy fuerte en la abeza, que estoy estudiando. Graias por haer mi día a
día menos gris, y mis nes de semana más ajetreados.
En esta ategoría entran también un buen puñado de gente del IFAE, `los del
instituto de al lado'. A los seniors, graias por aguantar estoiamente mis inesantes
dudas, ruegos y preguntas, en espeial a Stefan, Daniel y Abelardo. De los niños no
me olvido, por supuesto, también les doy las graias: Manel (por darme ollejas y
animarme, todo a la vez: volveré a visitarte y es una amenaza), Ignasi (por haerme
temer más que antes los petardos y adorar más que antes la montaña), Roberta (mi
`riatura' y ompañera en desgraias, la tesis se aaba pero nosotras no), sin olvidar
a las reientes inorporaiones, Aliia (a.k.a. la piraña más diharahera, ojalá nos
hubiéramos enontrado antes, niña) y Adiv (ompi de piso durante 6 meses, que
tiene su mérito). Y ya que estoy, también aproveho a mandar un abrazo enorme a
esa omunidad de italianos que me han heho onoer más lugares de esta iudad
que ualquier persona loal: me alegro de que nos hayáis
invadido.
Y antes de que deje de hablar del trabajo, quiero reonoer aquí la labor de
Isabel, Del y Josep. Desde la administraión, la gestión o la informátia, se han
oupado de mí y me han ayudado on la mejor de las inteniones siempre que han
podido, y más allá de lo que les toaba. Y a Alina, que no se me olvida, graias por
nuestras harlas diarias aguantando tormentas y tempestades, y por ser la primera
en leerse esta tesis y orregir mi inglés para que fuera más failmente legible. Los
errores que queden son míos.
Llegados a este punto, tengo que parar de haer listas.
En los onursos y
entregas de premios se llama a esta ategoría `meniones espeiales', y omo tal
deben onsiderarse. Ellos me han ambiado para bien, espero, y graias a ellos he
llegado a donde estoy. Esribir esta tesis no ha sido sólo aumular onoimientos
en astrofísia.
Mi salud mental se ha visto laramente resentida, y de no ser por
ellos, llevaría ya una bonita amisa blana, on mangas atadas a la espalda. Graias
por estar a mi lado todos estos años, y por uidar, omo bonus extra, de mi salud
emoional.
A Carlos, le doy las graias por nuestras inaabables onversaiones
sobre libros, pelíulas, omis y demás, pero sobre todo por reordarme que valgo
más de lo que reonozo, y por tratar de enseñarme a quererme un poo más.
Tengo tus palabras en la mente, apliarlas me llevará tiempo, pero que sepas que
tendrás una gran parte de ulpa uando lo onsiga.
A Del, por ser mi amiga
y ompartir onmigo el troito de su vida que he tenido la suerte de preseniar,
peluquera inluida. Suya es la ulpa de que en estos agradeimientos inluya una
de las frases on más sinsentido de la historia: graias por ayudarme a apreiar el
inestimable uso de una bola de demoliión, por mostrarme la verdad que esonde
la palabra perro omo deniión de jornada laboral, y por haerme entender que la
vida sería muho más triste sin pingüinos ni ovejas. Reuerda lo que dijo el telar
del destino. . . A Daniela, por onvertirse en mi
maligna aprendiz
y sufrir uando he
sufrido y reir uando yo he reído. Pink girl, loa-loa-loa, no defraudes al LOC (que
te ayude Aliia, es su deber pirañil). Volveré y tendremos esta, salsa y elefantitos
de olores.
Cambio de iudad y me vuelvo a Madrid, aunque sea sólo on la mente: mis
v
amigos no me han olvidado en este tiempo, y omo en ada separaión me he dado
uenta de la suerte que tengo onoiendo gente. Con ada regreso, he podido robaros
minutos, risas y muhos ánimos. Desde aquí, os doy las graias: a los del master, por
ser los
afetados
que mejor saben salir de ena y bares (Cris, Álvaro, Ignaio, Pablo y
Juan-ito), a los del barrio, por aogerme on tanto ariño desde el primer día (Jewi,
Riki, Guille, Fer,
et al.),
y a los de la arrera, porque ya sois mis amigos de verdad
y uento on vosotros (Arturo, Carmen, Ele-rizos, Fer, Juan, Marta, Sol, Super-Ele,
váis por orden alfabétio, ea). Y ya para terminar, agradeer de todo orazón, y me
da igual que suene ursi, a la piedra angular en mi vida que onstituyen las tres:
Ana, Isa y Elena.
Cada una guardáis una parte diferente de mí, sois las mejores
amigas que podría haber soñado, y ualquier osa que diga sonará a poo. Graias,
de verdad.
Everyone seems quite relieved, though,
onsidering they all knew I'd get o.
J. K. Rowling,
Harry Potter and the Order of the Phoenix
Por último, y por tanto más importante, quiero darles las graias a mi familia.
Tanto a los que me aogieron a mi llegada a Barelona omo a una más, omo a
los que me han seguido animando desde Madrid. Tengo muha suerte de teneros,
y está laro que seguiremos unidos sin importar dónde esté. De todos ellos quiero
destaar a mi padre, a mi madre y a mis hermanos.
Mis palabras no van a ser
suientes, pero lo voy a intentar. Mis padres han sido y seguirán siendo mi lugar
seguro en el mundo. Desde el prinipio me han apoyado en mi eleión, aunque ello
supusiera mandarme a 600 km de asa que era 600 km más lejos de lo que ellos
hubieran deseado. Pero siempre han estado ahí para mí, y siempre los he sentido
era. Estoy orgullosa de la forma en la que me habéis riado, y espero que vosotros
lo estéis de mí. A mi hermano Pablo le doy las graias por seguir onando en mí,
aunque me fuera lejos. . . justo después de embararle en la loura de la Físia. Y a
mis enanitos, Jorge y Luis, que después de tanto tiempo ya no son tan pequeños,
también les quiero dar las graias por llenarme de abrazos y besos on los que llenar
mis largas ausenias. Os quiero muho, a todos. Graias.
There's no plae I an be
sine I found
serenity.
You an't take the sky from me.
Joss Wheddon,
Firey
Contents
1 Introdution
1
1.1
Conneting CR and gamma rays
1.2
Gamma-ray Astronomy, There and Bak Again
1.3
. . . . . . . . . . . . . . . . . . . .
1
. . . . . . . . . . . .
4
1.2.1
Observing photons of GeV energies . . . . . . . . . . . . . . .
4
1.2.2
Observing photons of TeV energies
. . . . . . . . . . . . . . .
7
. . . . . . . . . . . . . . . . . . . . . . . . .
8
Reent sienti impat
1.3.1
A brief summary of galati highlights
. . . . . . . . . . . . .
1.3.2
A brief summary of extragalati highlights
8
. . . . . . . . . .
11
1.4
Multimessenger astronomy . . . . . . . . . . . . . . . . . . . . . . . .
13
1.5
On this Thesis
15
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
2 Diusion of osmi-rays
2.1
The role of diusion
. . . . . . . . . . . . . . . . . . . . . . . . . . .
20
2.2
Astrophysial senarios in the Pre-Fermi era . . . . . . . . . . . . . .
22
2.2.1
2.3
Disussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Moleular louds illuminated by CRs from SNRs
. . . . . . . . . . .
3 Pre-Fermi study on the environment of SNR IC443
25
28
31
3.1
IC443 plaed into ontext
. . . . . . . . . . . . . . . . . . . . . . . .
31
3.2
MAGIC and EGRET observations of the region . . . . . . . . . . . .
34
3.3
A model for MAGIC J0616+225
. . . . . . . . . . . . . . . . . . . .
35
Results of the model . . . . . . . . . . . . . . . . . . . . . . .
35
3.4
Disussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
3.5
Summary
40
3.3.1
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 The GeV to TeV onnetion in SNR IC 443
4.1
41
New high and very high-energy observations . . . . . . . . . . . . . .
41
4.1.1
Relative loalization of soures
42
4.1.2
Possible relationship between gamma-ray emission and the PWN 43
. . . . . . . . . . . . . . . . .
4.2
Comparison with nominal model
4.3
Using
4.4
Cosmi-ray distributions and their eets
4.5
Degeneraies and unertainties
Fermi
. . . . . . . . . . . . . . . . . . . .
LAT data to onstrain model parameters
4.5.1
Inuene of the
4.5.2
43
. . . . . . . .
45
. . . . . . . . . . . . . . .
46
. . . . . . . . . . . . . . . . . . . . .
49
δ-parameter
. . . . . . . . . . . . . . . . . . .
50
Unertainties due to the ross setion parameterization . . . .
51
4.6
Computation of seondaries other than photons . . . . . . . . . . . .
54
4.7
Conluding remarks
55
. . . . . . . . . . . . . . . . . . . . . . . . . . .
viii
Contents
5 Starburst galaxies
57
5.1
Introdution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
57
5.2
Theoretial model
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
58
5.3
M 82 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
62
5.3.1
Comparison with previous studies . . . . . . . . . . . . . . . .
63
5.3.2
Results and Disussion . . . . . . . . . . . . . . . . . . . . . .
64
Disovery of HE and VHE emission from starbursts . . . . . . . . . .
74
5.4.1
Gamma-ray emission deteted from M82 . . . . . . . . . . . .
74
5.4.2
NGC 253, onfronted with the model . . . . . . . . . . . . . .
74
5.4
5.5
Conluding remarks
. . . . . . . . . . . . . . . . . . . . . . . . . . .
6 Analysis of MAGIC data
6.1
6.2
6.3
77
83
Cherenkov tehnique and telesopes . . . . . . . . . . . . . . . . . . .
83
6.1.1
Cherenkov light . . . . . . . . . . . . . . . . . . . . . . . . . .
84
6.1.2
Hadroni and eletromagneti showers
. . . . . . . . . . . . .
85
6.1.3
Imaging Air Cherenkov Tehnique
. . . . . . . . . . . . . . .
86
The MAGIC telesopes . . . . . . . . . . . . . . . . . . . . . . . . . .
88
6.2.1
Struture and reetor . . . . . . . . . . . . . . . . . . . . . .
88
6.2.2
Camera
89
6.2.3
Readout, trigger and data adquisition
6.2.4
Calibration
6.2.5
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . .
90
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
91
Observation modes . . . . . . . . . . . . . . . . . . . . . . . .
91
Analysis method
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
91
6.3.1
Mono observations
. . . . . . . . . . . . . . . . . . . . . . . .
96
6.3.2
Stereo observations . . . . . . . . . . . . . . . . . . . . . . . .
100
7 MAGIC upper limits in the region of SNR G65.1
101
7.1
Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
101
7.2
Observations
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
103
7.3
Data analysis
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
104
7.4
Upper limits on the gamma-ray ux
7.5
Interpretation and disussion
7.6
Conlusions
. . . . . . . . . . . . . . . . . .
106
. . . . . . . . . . . . . . . . . . . . . .
109
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
110
8 Simulations of CTA response to partiular siene ases
111
8.1
Sorting out dierent layouts and ongurations for CTA
. . . . . . .
111
8.2
A brief look at starting-up tools . . . . . . . . . . . . . . . . . . . . .
113
8.3
Spetral studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
115
8.4
8.3.1
Moleular louds illuminated by CR from nearby SNR . . . .
116
8.3.2
Starburst galaxies M82 & NGC 253
. . . . . . . . . . . . . .
118
Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
120
Contents
ix
9 IC 443 in MAGIC stereo and prospets with CTA
9.1
Proposal and observations with MAGIC stereo
9.2
Analysis and results
9.3
IC443 as seen in CTA
. . . . . . . . . . . .
125
128
. . . . . . . . . . . . . . . . . . . . . . . . . . .
129
. . . . . . . . . . . . . . . . . . . . . . . . . .
131
10 Conlusions and future work
137
10.1 Final remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
137
10.2 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
138
Bibliography
141
List of Figures
169
List of Tables
179
Chapter 1
Introdution
Contents
1.1 Conneting CR and gamma rays . . . . . . . . . . . . . . . .
1.2 Gamma-ray Astronomy, There and Bak Again . . . . . . .
1
4
1.2.1
Observing photons of GeV energies . . . . . . . . . . . . . . .
4
1.2.2
Observing photons of TeV energies . . . . . . . . . . . . . . .
1.3 Reent sienti impat . . . . . . . . . . . . . . . . . . . . . .
7
8
1.3.1
A brief summary of galati highlights . . . . . . . . . . . . .
8
1.3.2
A brief summary of extragalati highlights . . . . . . . . . .
11
1.4 Multimessenger astronomy . . . . . . . . . . . . . . . . . . . . 13
1.5 On this Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.1 Conneting CR and gamma rays
Gamma-ray astronomy appeared as a mean to obtain an answer for the long-standing
problem of the origin of osmi rays (CR). Those CR partiles were disovered by
Vitor Hess in 1912, who observed an ionizing radiation impating on nulei in the
Earth's atmosphere [Hess 1912℄. The CR spetrum, shown in Figure 1.1, extends
over an energy range of 13 orders of magnitude.
Below
E = 1 GeV,
the CR ux is aeted by the solar wind, via the 11 yrs
modulation of its magneti eld. At higher energies the dierential spetrum an
be desribed by a power law
15.5 eV and
to E = 10
Γ ≈ 3.0
dN/dE ∝ E −Γ
with a spetral index
above that energy.
`knee'. The spetrum hardens again at about
Γ ≈ 2.7
up
The transition region is alled
E = 1018 eV (the
so-alled `ankle'). It
is believed that CRs below the `knee' are produed at galati sites like supernova
remnants, pulsars, or binary systems, while CRs with higher energies are more likely
extragalati. Due to galati and intergalati magneti elds, harged osmi rays
up to
1019 eV
are isotropized. Therefore, their arrival diretion at Earth does not
point bak to their origin. Only at even higher energies, in the regime of the ultra
high energy osmi rays, the rigidity
R = E/(Ze)
of the partiles is so high that
they are not deeted by extragalati or galati magneti elds (rgyro
= R/B ).
The osmi-originated partiles an be eletrially harged (eletrons, protons,
heavy nulei, . . . ), but there is also photons.
Sine photons do not have harge,
they are not deeted by the interestellar magneti elds, thus providing diret
2
Chapter 1. Introdution
Figure 1.1:
All-partile osmi ray spetrum. From [Beker 2008℄.
information on the loation of the original soure.
These energeti photons are
produed through several non-thermal proesses and, depending on the nature of
the parental osmi-ray partile, they an be either leptoni (mostly eletrons) or
hadroni (mostly protons and nulei) proesses.
The main physial proesses that ontribute to gamma-ray reation by eletrons
and other partiles alike are:
synhrotron radiation, uvature radiation, inverse
Compton interations, relativisti bremsstrahlung and eletron-positron annihilation. Whereas for proton-originated gamma rays there are: photomeson prodution
and neutral pion deay from proton-proton (pp ) interations. For a omprehensive
study on the details of these proesses see [Ginzburg & Syrovatskii 1964℄, a general
sketh an be seen in Figure 1.2. Essentially the proesses an be briey desribed
as follows.
Synhrotron radiation
Extremely energeti partiles moving in a strong magneti eld will emit
gamma-ray photons within an angle
θ ∼ mc2 /E
of its diretion of motion.
Synhrotron radiation usually generates seed photons for inverse Compton
sattering (see below). Moreover, ultra-high energy CRs an emit synhrotron
photons diretly in the gamma-ray energy domain.
Curvature radiation
Inside strong magneti elds harged partiles move along the eld lines and
are aelerated (beause the urvature radius of the eld is small) and then
radiate.
Inverse Compton interation
Relativisti eletrons are sattered on soft photons, transfering part of their
energy, thus being able to produe gamma rays. Two regimes an be onsidered
1.1. Conneting CR and gamma rays
3
Figure 1.2: Main physial proesses that an generate gamma-ray photons through
dierent interationsm, both hadroni (b) and leptoni (, d, e). Annihilation an
take plae among leptons or hadrons.
Ee Eγ ≪ m2e c4 ) and
2 4
For Ee Eγ ≈ me c , the
for the ross-setion of the interation: the Thompson (for
the KleinNishina (for
Ee Eγ ≫ m2e c4 )
approximation.
exat Klein-Nishina formula should be used, see (Weinberg 1995, pp.362).
σT
σKN
=
2
3
8 πre
(1.1)
Eγ
1
= πre2 (ln(2ε) + 0.5) , ε =
ε
me c2
(1.2)
Photomeson prodution
Interation of a very relativisti proton with a photon produe pions.
This
proess is responsible for the GZK ut-o at distanes above 100 Mp.
Relativisti bremsstrahlung
A relativisti eletron is aelerated in the eletrostati eld of a nuleus or a
harged partile, radiating energeti photons. The emitted photon spetrum
an be expressed with a power law with the same index as the aelerated
eletron.
Hadroni gamma-ray emission
The ollision of two protons (or proton antiproton) produe neutral and
harged partiles.
The neutral pions deay inmediately (∼
gamma-ray photons. The harged pions also deay fast (∼
10−16 )
in two
10−8 ), generating
muons and neutrinos. The former seondaries, the muons, also deay produing eletrons (or positrons, depending on the harge of the original muon and
4
Chapter 1. Introdution
pion) and neutrinos (or antineutrinos). This neutrino signature is harateristi and unique for hadroni interations.
π 0 → 2γ
π ± → µ± + ν
µ± → e± + ν + ν
Eletron-positron annihilation
Two gamma rays are produed when an eletron and a positron ollide and
annihilate.
1.2 Gamma-ray Astronomy, There and Bak Again1
In the early years of gamma-ray astronomy, the suess of a mission over its preedents was quantied by the number of photons, rather than the soures deteted.
The rst experiments devoted to observe energeti photons in the MeVGeV range
were plaed in balloon- and spae-borne detetors.
However, gamma rays above
hundreds of GeV ould not be deteted by these detetors mainly due to their small
olletion area. Ground-based telesopes over this range of energies, for instane,
proting from the imaging Cherenkov tehnique, or deteting other seondary partiles that arry information of the primary osmi ray.
1.2.1 Observing photons of GeV energies
Although several gamma-ray detetors were plaed into spae in the 1950's and
1960's, the rst suesful sienti mission dediated to the study of gamma
rays was launhed in 1972.
The seond Small Astronomy Satellite (SAS-2) only
operated for 7 months, but in that short time it deteted photons above 30 MeV
from the Crab and Vela pulsars, and onrmed the Galati enter as a soure of
gamma rays. Shortly afterwards, in 1975, the COS-B satellite started taking data at
energies above 50 MeV. For the rst time, the COS-B mission ompleted a skymap of
the Galati plane between 100 MeV and 6 GeV, allowing the study of the large-sale
gamma-ray diuse emission.
This diuse emission was supposed to be originated
from osmi rays interating with the interestellar medium and, in fat, a orrelation
with gas distribution (both in HI and CO maps) was found.
Emission ould be
resolved from loud omplexes as Ophiuhus and Orion-Monoeros. Moreover, the
Crab and Vela pulsars were onrmed as gamma-ray soures, as well as the yetunidentied Geminga soure and the Cygnus region [Hermsen 1990℄. Moreover, the
rst extragalati soure at these high energies was deteted: the quasar 3C 273.
However, the large positional unertainty from 0.4 to 1.5 degrees, depending on
the energy prevented further identiation of point-like soures.
1
The Hobbit, or There and Bak Again, better known by its abbreviated title
fantasy novel by J. R. R. Tolkien, published in 1937.
The Hobbit
, is a
1.2. Gamma-ray Astronomy, There and Bak Again
5
Figure 1.3: Skymap above 100 MeV from our Galaxy by the entire EGRET mission
(phases 1 to 4), with the main soures deteted in gamma rays. Credit: EGRET
Team/NASA.
Following these enouraging results, other satellites were launhed during the
next deade.
The next gamma-ray experiment, the Energeti Gamma-Ray Ex-
periment Telesope (EGRET), on board of the Compton Gamma-Ray Observatory (CGRO), was launhed in 1991.
After nine years of observations be-
tween 30 MeV and 30 GeV, EGRET left behind a atalog ontaining 271 soures
[Hartman
et al.
emitters.
Pulsars were also established as a soure lass by adding 5 new mem-
1999℄. Blazars were established as the more numerous gamma-ray
bers, inluding the identiation of Geminga, a radio-quiet pulsar.
The skymap
of the Galaxy is shown in Figure 1.3 and presents some of the prinipal identied
soures. Among them, the Large Magellani Cloud (LMC) is the rst galaxy deteted in gamma rays without having an ative galati nulei (AGN). Moreover,
the radio galaxy Centaurus A (Cen A) is also deteted.
soures in the Third EGRET Catalog (∼
170)
Nonetheless, 60% of the
are unidentied.
Studies on the
galati diuse emission were arried on thanks to the performed all-sky survey.
Together with this, the telesope allowed determining the isotropi nature of the
extragalati diuse emission. Another sienti ontribution provided by EGRET
was the prolonged GeV emission (or high energy tail) deteted from gamma-ray
bursts. Regarding aveats of this instrument, the derease of detetion eieny at
high energies and the large error boxes that prevented from nding ounterparts for
some of the unidentied soures are among the most importants.
Almost a deade after the end of the CGRO mission in 2000, AGILE and
Fermi
6
Chapter 1. Introdution
Figure 1.4:
All-sky map above 300 MeV during the rst year of the
telesope. Credit: NASA/DOE/Fermi LAT Collaboration.
Table 1.1:
GeV range:
Fermi
LAT
Mission parameters of the three latest spae telesopes in the MeV EGRET, AGILE and
Fermi
LAT. The sensitivity above 100 MeV is
onsidered for a 2-year survey at high latitudes.
Energy range
Energy resolution
Eetive area (peak)
Field of view
Angular resolution
Sensitivity > 100 MeV
Mass
EGRET
30 MeV 30 GeV
20 25%
1500 m2
0.5 sr
5.5◦ at 100 MeV
0.5◦ at 10 GeV
10−7 m−2 s−1
1800 kg
AGILE
30 MeV 50 GeV
∆E/E = 1
700 m2
3 sr
4.7◦ at 100 MeV
0.2◦ at 10 GeV
5 × 10−8 m−2 s−1
60 kg
LAT
20 MeV 300 GeV
18 6%
10000 m2
2.4 sr
3.5◦ at 100 MeV
0.15◦ at 10 GeV
2 × 10−9 m−2 s−1
3000 kg
Fermi
have been launhed in 2007 and 2008, respetively. AGILE (Astrorivelatore Gamma
a Immagini LEggero) ontains an X-ray monitor observing from 18 to 60 keV and a
gamma-ray telesope that overs the sky in the energy range from 30 MeV to 50 GeV.
The two instruments on board of
Fermi
are a Gamma-ray Burst Monitor (GBM),
sensitive to hard X-rays and soft gamma-rays, and a Large Area Telesope (LAT)
that observes in sky-survey mode from 20 MeV to 300 GeV. Table 1.2.1 ompares
the parameters of the latest three satellite telesopes. Already in the rst year of
observation (Figure 1.4),
Fermi
LAT deteted around 1451 soures, inluding new
types of gamma-ray emitters, i.e., pulsar wind nebulae, supernova remnants, X-ray
binaries, starburst galaxies and globular lusters. The inreased angular resolution
has nally allowed to arry on morphologial and spetral studies of individual
soures. Key results provided by these latest experiments are disussed in the next
setion.
1.2. Gamma-ray Astronomy, There and Bak Again
7
The detetion tehnique ommon to SAS-2, COS-B, EGRET, AGILE and
Fermi
LAT onsist in pair-prodution telesopes with a traker, a alorimeter and an antioinidene detetor. The eletron and positron generated by the original gamma
ray hits the silion-trip detetor, and the paths are traked through the dierent
layers. The pair onversion signature is also used to distinguish the signal from the
more abundant bakground of osmi rays. The energy of the partile is measured
in the alorimeter, when it is totally absorbed. The ultimate defense against the CR
bakground is the antioinidene detetor that overs the traker. Flashes of light
are produed whenever a harged partile hits on it. All the information olleted
from the previous omponents is handled by the data aquisition system (DAQ),
whih also tells apart CRs from gamma rays for the rst time.
1.2.2 Observing photons of TeV energies
Above 100 GeV, the ux of gamma rays is too low for the small olletion area of
the spae-borne telesopes to detet them.
Nonetheless, the Earth's atmosphere,
that prevents the primary gamma-ray photons to arrive at ground level, also ats
as a alorimeter where a asade of partiles reated by energeti osmi partiles
develops. The seondary partiles that are generated in this way an be deteted
from ground-based telesopes and provide information from the primary partile,
like the arrival diretion and the primary energy.
One of the existing tehniques
prots from the Cherenkov radiation: when the gamma-ray photon enters the atmosphere, it generates an eletromagneti asade (eletron-positron pair), then,
the seondary partiles propagate at a faster-than-light speed in the medium, generating a ash of Cherenkov light that reahes ground level (see Chapter 6 for more
details in Cherenkov tehnique and detetion).
Gamma rays and harged osmi rays an both produe partile asades in
the atmosphere, being the latter several orders of magnitude more numerous and
thus produing an overall bakground.
The imaging tehnique tries to disrimi-
nate among both kind of partiles through geometri onsiderations on the shape
of the asade when it arrives at the detetor.
In 1989, the 10-meter Whipple
telesope pioneered this tehnique and deteted the Crab Nebula at TeV energies
[Weekes
et al.
1989℄. The seond generation of Cherenkov telesopes in the 90's was
leaded by the High Energy Gamma Ray Astronomy (HEGRA) and Cherenkov Array at Th'emis (CAT) experiments.
They were responsible of deteting the rst
extragalati soure at TeV energies, the blazar Mkn 421 [Punh
et al.
1992℄, and a
few other galati and extragalati soures (like, for instane, the SNR Cas A and
the blazar Mkn 501).
The Imaging Air Cherenkov (IAC) telesopes improved the bakground rejetion
through stereosopi observations.
The introdued progress relied on the better
determination of the point of the atmosphere where the primary photon impat, the
diretion where it ame from and the original energy. At present, the three main
IAC telesopes are:
•
High Energy Stereosopi System (H.E.S.S.) operating sine 2004 with 4 tele-
8
Chapter 1. Introdution
Table 1.2: Performane of the three main Cherenkov experiments in the GeV TeV
range: H.E.S.S., MAGIC and VERITAS. In the title:
of telesopes, Tels.
♯
Tels.
Area is the area of eah telesope, f.o.v.
stands for number
is the eld of view,
Tot. Area is the total area of the array of telseopes, Eth is the energy threshold,
Ang.
res.
means angular resolution, and Sensitivity 50 h onveys the soure ux
in 50 hours of observation respet to the Crab Nebula ux with a signiane of 5
sigma. From [De Angelis 2011℄.
Instrument
♯ Tels.
H.E.S.S.
MAGIC
4
2
Tels. Area
(m2 )
107
236
VERITAS
4
106
f.o.v.
(◦ )
5
3.5
Tot. Area
(m2 )
428
472
4
424
Eth
(TeV)
0.1
0.05
(0.025)
0.1
Ang. res.
(◦ )
0.06
0.07
Sens. 50 h
(% Crab)
0.7
0.8
0.07
0.7
sopes, of 13 m diameter eah, in Namibia (South Afria).
•
Major Atmospheri Gamma-ray Imaging Cherenkov Telesope (MAGIC) onsisted on a single-dish telesope by 2004, and then beome a stereosopi
system by adding a seond telesope in 2009. Both telesopes have a diameter
of 17 m and are loated in La Palma (Canary Islands, Spain).
•
Very Energeti Radiation Imaging Telesope Array System (VERITAS) observing with 4 telesopes, 12 m diameter eah, sine 2007.
The reent re-
arrangement of the array improved signiatively its sensitivity.
Further information on their perfomane are displayed in Table 1.2.2.
In addition to these experiments, there are other ways to observe at TeV energies
from ground level: for instane, deteting the seondary partiles generated in the
mentioned atmospheri asades. These experiments have higher energy thresholds
and longer duty yles than IAC telesopes (whih annot observe during full Moon).
Tibet and Milagro are the best examples of air shower detetors.
1.3 Reent sienti impat
In the past few years, the latest instruments mentioned in the previous setion have
provided the sienti ommunity with key results from the gamma-ray astronomy,
from GeV to TeV energies.
1.3.1 A brief summary of galati highlights
Supernova remnants (SNRs) have always been the most favoured andidates for
aelerating osmi rays, and thus an expeted soure of gamma rays at high and
very high energies (HE and VHE, respetively).
In fat, suh emission has been
1.3. Reent sienti impat
Figure 1.5:
Left:
9
Skymap RX J1713.7-3946 by H.E.S.S., blak ontours over-
plotted show the X-ray brightness that ASCA detetes from 1 to 3 keV. From
[Aharonian
et al.
2004b℄. Right:
Fermi
LAT spetral energy distribution (SED) of
the SNR W44, eah urve orresponds to
π0
deay (solid), eletron bremsstrahlung
(dashed), inverse Compton sattering (dotted) and bremsstrahlung from seondary
eletrons and positrons (thin dashed). From [Abdo
et al.
2010f℄
reported, although the nature of the parental osmi-ray partiles that are aelerated (protons or eletrons) still remains a subjet of debate.
The biggest step
towards the disentanglement of hadroni/leptoni senarios has been the spatial
resolution of shell-like SNR, reported both at GeV and TeV energies. RX J1713.73946 [Aharonian
et al.
2004b℄ and W44 [Abdo
et al.
2010f℄ onstituted the pioneer-
ing soures in eah energy regime.
The rst onrmed shell-like SNR, RX J1713 in short, was deteted and spatially
resolved by H.E.S.S. [Aharonian
et al.
2004b℄. The unpreedently well-resolved shell
morphology, aquired thanks to the stereosopi imaging tehnique, oinides with
the X-ray morphology, as an be seen in Figure 1.5 (left). The observed TeV spetrum (without signs of a uto up to several TeVs) indiates that partiles are being
aelerated in the shell of the SNR to energies up to 100 TeV. To further distinguish
between protons or eletrons as the parent partiles produing gamma rays, observations of SNRs on the GeV energy range are needed.
resolved the shell morphology of the SNR W44 [Abdo
The Fermi LAT detetor
et al.
2010f℄, and presented
its spetrum with a low energy ut-o (around 2 GeV), as seen in Figure 1.5 (right).
Subsequent detetions of both young and middle-aged SNRs ontinue to provide
information on their emission mehanism.
Not only expeted gamma-ray emitters have been deteted and studied, but
also other type of objets have surprised the sienti omunity by showing gammaray emission. This has been the ase of the nova that was found in the symbioti
binary V407 Cygni (a binary system onsisting on a pulsating red giant and a
white dwarf ompanion).
The
Fermi
LAT reported HE emission oiniding with
the maximun optial emission from a nova outburst [Abdo
et al.
2010e℄. The GeV
emission lasted for 2 weeks, by that time, the X-ray emission reported by Swift
started rising. The gamma-ray spetrum suggest for the emission to be produed
10
Chapter 1. Introdution
either by neutral pion deay or by inverse Compton sattering of infrared photons
from the red giant. A predition for novas in the gamma-ray sky was previously made
by [Tatishe & Hernanz 2007, Tatishe & Hernanz 2008℄, although the position
on the sky of the studied soue prevented observations of gamma rays with groundbased detetors. Notwithstanding, these gamma-ray novae are thought to be rare
events.
Another lass of long expeted gamma-ray generators are the X-ray binaries
(XRBs). The rst one ever deteted was Cygnus X-3 (Cyg X-3), by SAS-2. But it
was only reently that it has been onrmed as a gamma-ray soure between 100 MeV
et al. 2009g℄. Furthermore, the rst
XRB deteted at TeV energies was PSR B1259−63 [Aharonian et al. 2005a℄, very
losely followed by the detetion of LS 5039 by H.E.S.S. [Aharonian et al. 2005℄.
and 100 GeV by the
Fermi
satellite [Abdo
The next year, another TeV objet was added to this lass when LS I +61 303
[Albert
et al.
2006℄ was deteted by the MAGIC telesope. In eah ase, the gamma-
ray emission appear to be modulated by the orbit of the system. The aeleration
site of the parental osmi ray partiles that produe the gamma-ray emission seems to be geometry dependent and onned inside the binary system. Nonetheless, one of the open disussions regarding XRBs is the nature of the ompat objet:
wheter it is a blak hole or a neutron star. In the former senario, the binary system
is alled
miroquasar
and it displays relativisti radio jets. Hene, the VHE gamma
rays may be produed in the jet via inverse Compton sattering.
In the ase of
the pulsar binary system, the VHE gamma rays are expeted to be generated in
the wind-wind ollisions between the pulsar and the massive ompanion star. The
multiwavelength approah to solve the puzzle would be either deteting the jet in
radio, or pulsations from the ompat objet. Up to date, 7 XRBs have reported
et al. 2010i℄, Cyg
et al. 2010℄, 1FGL
either at GeV or TeV energies, adding PSR B1259−63 [Abdo
X-3 [Abdo
et al.
2009g℄, Cyg X-1 [Albert
J1018.6-5856 [Corbet
et al.
et al.
2007a, Sabatini
2011℄ and HESS J0632+057 [Ong 2011, Mariotti 2011℄
to the already mentioned binary systems. It is worth noting that, of these soures,
only LS I +61 303, LS 5039 and PSR B12594−63 have been deteted at both GeV
and TeV energies.
Diuse emission from the Galati Center has been observed sine the begining
of the spae-borne missions. This emission was assoiated with interations of CR
with the interestellar medium. Thanks to the san of the Galati Plane performed
by H.E.S.S. [Aharonian
et al.
2005b℄, eight new soures were disovered. In deeper
and longer observations, the aorementioned assoiation speially, to dense
moleular louds ould be suessfully proved [Aharonian
et al.
2006e℄. Therefore,
hadroni proesses are favoured as the origin of the gamma-ray emission in the enter
of our Galaxy.
The latest ares measured in the Crab Nebula [Abdo
et al.
2011℄, defy the deni-
tion of this objet as the 'standard andle' both in X-ray and gamma-ray astronomy.
In X-rays, variation in the ux of the Crab Nebula have been reported for the last
years. The gamma-ray ares deteted by the
Fermi
and AGILE satellites, however,
are not orrelated with the emission in the keV energy regime.
1.3. Reent sienti impat
11
Pulsars, the rst established soure-lass in gamma-rays, are starting to be studied as a population in gamma rays.
Fermi
LAT deteted more than 60 of these
objets, from whih 8 were milliseond pulsars (MSPs) [Abdo
et al.
2009e℄, and 16
2 searhes [Abdo
new gamma-ray pulsars were found through blind
et al.
2009a℄.
The starting point of these disoveries was starred by the pulsar found inside the
SNR CTA [Abdo
et al.
2008℄. CTA-1 belongs to a ertain type of radio-quiet, but
gamma-ray-loud pulsars, like Geminga.
The MSPs are usually found in binary systems and thougth to be spun up by the
torque resulting from aretion of mass from their ompanion. They are signiantly
more stable than younger pulsars, although their basi emission mehanism seems
to be the same.
The globular luster 47 Tuanae [Abdo
et al.
2009f℄ belongs to
another lass of predited soure of gamma rays, but it had eluded detetion until
very reently. Globular lusters ontains a large amount of MSPs, and in fat their
GeV emission is largely explained by the umulative gamma-ray emission from these
young pulsars.
Furthermore, in 2008, MAGIC opened the window of the detetion of pulsars from
[Aliu
et al.
ground-based
telesopes:
the
Crab pulsar
2008b℄, thanks to a speial trigger setup.
was seen above
25 GeV
This re-opened a disussion
on models that were trying to explain the emission and mehanism of pulsars. Very
reently, the Crab pulsar as been deteted by VERITAS at the
Fermi
Symposium
(2010) at energies as high as 100 GeV, thus onstraining even more the model for
the mehanism of gamma-ray prodution.
1.3.2 A brief summary of extragalati highlights
Blazars are the most numerous population of gamma-ray soures, and are inluded
in the ategory of ative galati nulei (AGN) objets. They allow studies on the
extragalati bakground light (EBL), test general relativity, and shed some light
on the jet proesses ouring next to their entral blak holes.
The starlight emitted by galaxies and aumulated over time is largely assumed
to be the main ontributor for EBL. Another possible soure of this diuse extragalati emission was thought to be the emission oming from the rst stars, that
were formed in the early Universe: metal-free massive stars, known as
population III.
Given that diret measurements are not straightforward, observing distant objets speially, their absorbed spetra like blazars seems a better approah. Those absorption features are a onsequene of photon-photon ollision and pair prodution.
The original spetrum of the soure (named intrinsin spetrum) is thus modied
and depends on the spetral energy distribution (SED) of the EBL. This spetral
hange (steepening above 1 TeV) beomes more pronouned at larger redshifts. For
instane, the H.E.S.S. experiment disovered gamma-ray emission from the distant
blazars H 2356-309 and 1ES 1101-232, at redshifts z = 0.165 and 0.186, respetively [Aharonian
et al.
2006f℄. By assuming an intrinsi and reasonable spetrum
for both blazars, an upper limit on the EBL ould be derived. The EBL ux was
2
None of them were deteted previously in any other lower frequeny
12
Chapter 1. Introdution
onstrained to lower values, onsistent with the limit provided by the integrated
light of resolved galaxies, and it exluded a major ontribution from the rst stars.
Up to date, ontinued observations of these objets is further onstraining the shape
of the EBL.
Blazars owe their large number of detetions to the fat of having their jets
pointing towards us. Their TeV emission is due to the photons emitted in the jet
being boosted by relativisti eets. Besides blazars, there have also been gammaray emission reported from other AGNs, like the radio galaxies M87 and Cen A and
far-away radio quasar 3C 279.
In
the
[Hartman
GeV
et al.
regime,
Cen
A
was
1999℄, and later on the
aged its giant radio lobes [Abdo
et al.
deteted
Fermi
by
the
EGRET
satellite
LAT telesope onrmed and im-
2010d℄. Cen A is the nearest and one of the
brightest radio galaxies, and has also been monitored at radio wavenlenghts.
M87 is one of the best studied radio galaxies in almost every wavelength,
◦ from the our line
with a resolved jet (in radio, optial and X-ray) inlined 30
of sight. It is one of the best andidates to study the jet onnetion to the observed
gamma-ray emission. A rst hint of detetion was laimed by the HEGRA experiment [Aharonian
[Aiari
et al.
et al.
2003℄ and was nally onrmed above 730 GeV by H.E.S.S.
2009℄. The fast TeV variability in a daily sale reported in 2005
already pointed to a small emission region for the VHE radiation, in the immediate viinity of the entral supermassive blak hole.
Another rapid and strong
outburst in 2008 was reported by the MAGIC telesope, subsequently followed by
the VERITAS and H.E.S.S., a response that allowed a dense sampling of the event
[Aharonian
et al.
2006d℄.
All the previous VHE gamma-ray detetions, together
with the simultaneous high-frequeny radio overage provided by the Very Long
Baseline Interferometry (VLBI), further onstrained the VHE emission site to take
plae within the jet ollimation, in a region small even for the highly resolved radio
images.
The more distant extragalati objet deteted in gamma rays is the radio quasar 3C 279.
Its detetion in aring state by the MAGIC experiment im-
plied not only the rst report at VHE of a quasar, but also that the Universe
was more transparent to gamma-ray radiation than what was previously thougth
[Albert
et al.
2008a℄.
The year 2009 brought to the gamma-ray astronomy the addition of a new lass
of soure:
starburst galaxies were found to emit both at GeV and TeV energies
(see below). These long predited gamma-ray emitters are loated at intermediate
distanes between the already deteted LMC lose to our Galaxy and the distant
blazars, and are supposed to have intermediate gamma-ray luminosities. The produion of gamma rays in these galaxies was predited to ome from the aeleration
of CRs in SNRs and subsequent ollision with interestellar gas. An exess in gamma
rays is expeted at the entral region of starburst galaxies due to the harateristi
enhaned SN explosion rate, enhaned star formation rate and rih moleular gas
regions. More disussion on this topi is provided in Chapter 5.
The two
losest starburst galaxies that have been deteted are M82,
by
Declination [deg]
1.4. Multimessenger astronomy
H.E.S.S.
-25
NGC 253
-25.5
PSF
-26
-12.72900h50m
00h48m
00h46m
13
140
120
100
80
60
40
20
0
-20
-40
-60
-80
-11.059
Right Ascension
Figure 1.6: Left: Skymap NGC 253 by HESS. Right: Spetrum M 82 by VERITAS.
VERITAS [Aiari
et al.
2009a℄, and NGC 253, by H.E.S.S. [Aero
the TeV range, and both of them were deteted by
[Abdo
et al.
2010℄.
Fermi
et al.
2009℄ in
in the GeV range
The VERITAS Collaboration presented a spetrum above
700 GeV, see Figure 1.6 (left). H.E.S.S. showed that the gamma-ray emission omes
from the entral part of the starburst galaxy, see Figure 1.6 (right).
Gamma-Ray Bursts (GRBs) were established as extragalati transient soures,
due to its isotropi distribution on the sky by BATSE, on board of CGRO. Their
spetra helps onstraining EBL [Abdo
[Abdo
Fermi
et al.
2009b℄.
et al.
2009h℄ and, reently, quantum gravity
The GRB 090510 at a redshift z = 0.903 was deteted by
over a very broad energy range (from 8 keV to 31 GeV). Despite its distane,
the rising edge time of the burst varied less than 1 s over the entire energy range.
Many theories on quantum gravity predit Lorenz invariane violation (LIV) that
should be deteted as a delay: an energy-dependent variation in the rising edge time
of the burst. This delay was not deteted in this GRB 090510 and set the strongest
onstrain on the Lorenz invariane up to now: less than the Plank length divided
by 1.2 at 99% ondene level.
1.4 Multimessenger astronomy
Neutrinos are the ideal astronomial messenger.
Sine they interat weakly with
matter, they travel long distanes without being deeted by magneti elds and
arrying almost unbiased information of the soure that produes them. However,
their detetion on Earth is not so easy, basially for the same reason: their lak of
eletri harge results in very sare interations. Therefore, the neutrino detetors
need to be inmense enough to ollet suient statistis.
One of the strongest motivations to promote neutrino astronomy from the
gamma-ray astronomer perspetive is that deteting neutrinos from an astrophysial soure would provide univoal evidene for the hadroni prodution of gamma-
14
Chapter 1. Introdution
rays (see setion 1.1). The gamma-ray and neutrino astronomy shared a ouple of
ommon aims:
•
the study of the type of soures and mehanisms responsible of the osmi-ray
aeleration,
•
and the nature and distribution of dark matter.
The most prominent km
3 neutrino experiments are about to open this window.
The IeCube Neutrino Observatory, in the Antartia, has been ompleted reently
[Halzen & Klein 2010℄, thanks to the suess of its predeessor, Antarti Muon
and Neutrino Detetor Array (AMANDA). On the other side of the Earth, the Cubi Kilometer Neutrino Telesope (KM3NeT) will soon ontinue the eorts made
by the Astronomy with a Neutrino Telesope and Abyss Environmental Researh
(ANTARES) experiment in the Mediterranean sea. Being plaed in dierent hemispheres, they will be both omplementary.
As has been mentioned, the inmense
partile detetors IeCube and KM3NeT have their performane previously tested
in smaller detetors, (namely AMANDA and ANTARES respetively).
The neutrino detetion tehnique is based on apturing Cherenkov light, whih is
produed when these partiles interat with a nuleus in the ie or in the water. The
few interations that take plae reate muons, eletrons and hadrons in a asade
of partiles. The harged seondary partiles are the ones that radiate Cherenkov
light and penetrate deep into the ie/water. The diretion of the neutrino an be
derived from the light pattern, that is reorded by photomultipliers (PMTs). The
time of arrival and the digitized waveforms of the light ontains the information
to reonstrut the energy of the neutrino events, as well as their arrival diretions.
The largest soure of bakground for osmi neutrinos are the so-alled atmospheri
neutrinos: they ome from the deay of pions and kaons that were produed in
pp
interations in the atmosphere. The undesired radiation is present up to 1000 TeV,
but its ux an be alulated. The good angular resolution is provided thanks to
the big size of the detetors (in the ie, the mean free path for muons an reak
10 km).
IeCube ontains a total of 5160 digital optial modules, deployed on 86 vertial
strings, with 60 digital optial modules (DOMs) attahed at depths around 2000 m.
The oneptual design is ilustrated in Figure 1.7. The bulk of IeCube is sensitive
to neutrinos with energies above 100 GeV; the DeepCore inll array may observe
neutrinos with energies as low as 10 GeV. The IeTop surfae array, loated on
the ie above IeCube, onsists of 160 ie-lled tanks, eah instrumented with two
DOMs. It observes osmi-ray air showers with a threshold of about 300 GeV. The
early data from IeCube are very promising, and the detetor is observing over 10
000 neutrino events per year.
Also proting from the Cherenkov radiation and ontaining water detetors is
the Auger Projet, named after Pierre Auger, the Frenh sientist who rst investigated air showers. Atually, Auger is a hybrid experiment that ombines partile
and uoresene detetors. The partile detetor part of the array onsists of a total
1.5. On this Thesis
15
Figure 1.7: Atual design of the IeCube neutrino detetor with 5160 optial sensors
viewing a kilometer ubed of natural ie. The signals deteted by eah sensor are
transmitted to the surfae over the 86 strings to whih the sensors are attahed.
IeCube enloses its smaller predeessor, AMANDA. From IeCube Siene Team Franis Halzen.
of 1,600 tanks of water, of large apaity and sealed from external light ontamination. It is dotted with PMTs to detet the passage of air shower partiles through
their emission of Cherenkov light. The tanks are spaed in a huge grid as to allow
detetion of a single air shower by ve to ten detetor tanks. There is a set of four
arrays of uoresene detetor telesopes interspersed among the water tank grid.
There is one telesope array in the enter of the partile detetor grid, with the
other three eyes around the rim of the grid.
1.5 On this Thesis
This Thesis ontains some studies on aspets related to osmi-ray diusion.
It is presented in two parts, one desribing models on the phenomenology of
CR diusion (Chapters 2 to 5), and another that shows observations using the
MAGIC experiment and simulations of the future Cherenkov Telesope Array, CTA
(Chapters 6 to 9).
In the rst part, the general aepted theory on CR diusion
is introdued in Chapter 2.
From this starting point, a model is presented for
the environment of the SNR IC 443 on Chapters 3 and 4 in order to explain
the high-energy phenomenology, and it is ontrasted with urrent observations
of the soure.
The Chapter 5 ontains a multi-messenger model for the diuse
emission of the starburst galaxy M82.
The gamma-ray preditions are ompared
with the reent detetions in the GeV and TeV energy range. In the seond part,
16
Chapter 1. Introdution
the Cherenkov tehnique and the MAGIC experiments is desribed.
The upper
limits obtained with the MAGIC-I telesope from two Milagro-deteted Brigth
Fermi soures in the region of the SNR G65.1+0.6 are presented on Chapter 7. The
Chapter 8 ontains simulations of CTA and initial spetral studies on partiular
siene ases. Observations with MAGIC stereo on IC 443, together with preliminar
studies performed with CTA an be found in Chapter 9. Finally, the Chapter 10
ontains onlusions and advanes some future work.
Part of the work in this Thesis has already been published in refereed journals:
Diusion of osmi-rays and the Gamma-ray Large Area Telesope:
nomenology at the 1-100 GeV regime, [Rodríguez Marrero
et al.
Phe-
2008℄.
MAGIC J0616+225 as delayed TeV emission of osmi-rays diusing from SNR
IC 443, [Torres
The
et al.
to
TeV
[Rodríguez Marrero
et al.
The
[Torres
GeV
2008℄.
GeV
et al.
to
TeV
view
of
SNR
IC443:
preditions
for
Fermi,
2009℄.
onnetion
in
the
environment
of
SNR
IC
443,
2010℄.
Multi-messenger
[de Cea del Pozo
et al.
model
for
the
starburst
galaxy
M82,
2009b℄.
MAGIC Upper Limits for two Milagro-deteted, Bright Fermi Soures in the Region of SNR G65.1+0.6 (as one of the orresponding authors), [Aleksi¢
et al.
2010℄.
Moreover oral and poster ontributions have also been presented by the PhD
student:
Diusion of osmi-rays and gamma-ray soures, oral talk, VIII Reunión Cientía de la Soiedad Española de Astronomía, 2008, Santander (Spain).
Model analysis of the very high energy detetions of the starburst galaxies
M82 and NGC 253, poster, Fermi Symposium, 2009, Washington DC (USA)
[de Cea del Pozo
et al.
2009a℄.
First exploration of the spetral CTA response on moleular louds near
supernova remnants, oral talk, General CTA Meeting, 2010, Zeuthen (Germany).
More ontributions displaying several simulations with CTA an be found in the
following address:
http://www.ta-observatory.org/tawpwiki/index.php/PHYS-TLs-work.
PART I:
Studies on the phenomenology of osmi-ray diusion
Chapter 2
Diusion of osmi-rays
Contents
2.1 The role of diusion . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2 Astrophysial senarios in the Pre-Fermi era . . . . . . . . . 22
2.2.1
Disussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
2.3 Moleular louds illuminated by CRs from SNRs . . . . . . 28
It is ommonly aepted that supernova remnants (SNR) are one of the most
probable senarios of leptoni and hadroni osmi-ray (CR) aeleration. The partile aeleration mehanism in individual SNRs is usually assumed to be diusive
shok aeleration, whih naturally leads to a power-law population of relativisti
partiles. In the standard version of this mehanism, e.g. [Bell 1978℄, partiles are
sattered by magnetohydrodynami waves repeatedly through the shok front. Eletrons suer synhrotron losses, produing the non-thermal emission from radio to
X-rays usually seen in shell-type SNRs.
The maximum energy ahieved depends on the shok speed and SNR age as
well as on any ompeting loss proesses.
In young SNRs, eletrons an eas-
ily reah energies in exess of 1 TeV, and they produe X-rays.
Non-thermal
X-ray emission assoiated with shok aeleration has been learly observed in
many SNRs.
But in order to have an observational onrmation of protons and
other nulei being aelerated, partiularly, in order to be able to distinguish
this from leptoni emission, one should try and isolate the multi-messenger effets of the seondary partiles produed when the aelerated hadrons interat
in nearby moleular louds through
pp
ollisions. These ideas go bak, for instane,
to the works by [Dogel & Sharov 1990, Naito & Takahara 1994, Drury
Sturner
et al.
1997, Gaisser
et al.
1998, Baring
et al.
et al.
1994,
1999℄, among others. In fat,
more than 30 years ago, [Montmerle 1979℄ suggested that SNRs within OB stellar assoiations, i.e.
star forming regions with plenty of moleular gas, ould
generate observable gamma-ray soures.
A moleular loud being illuminated
by partiles that esaped from a nearby SNR ould then at as a target for
pp
interations,
greatly enhaning the gamma-ray emission,
ent works by [Gabii & Aharonian 2007, Gabii
Rodríguez Marrero
et al.
2008℄.
et al.
see,
e.g.,
2009, Casanova
the re-
et al.
2010,
Furthermore, observing gamma rays from louds
nearby SNRs, an provide feedbak on our knowledge of the diusion harateristis of the environment.
20
Chapter 2. Diusion of osmi-rays
As investigated by [Aharonian & Atoyan 1996℄, the observed gamma rays an
have a signiantly dierent spetrum from that expeted from the primary partile
population at the immediate viinity of soure (the SNR shok).
standard diusion oeient in the range
spetra as steep as
Jp (Ep ) ∝ E −2
Γ ∼ 2.3 − 2.6
δ ∼ 0.3 − 0.6
For instane, a
an explain gamma-ray
in soures with partiles aelerated to a power-law
if the target that is illuminated by the
π 0 -deays
is suiently far
away from the aelerator. Measuring gamma-ray emission around SNRs would then
allow to aquire knowledge of the diusion environment in whih the CRs propagate
at several kp from Earth.
EGRET was unsuessful in performing detailed studies of the gamma-ray sky
above 10 GeV, partly due to bak-splash of seondary partiles produed by highenergy gamma rays ausing a self-veto in the monolithi anti-oinidene detetor
used to rejet harged partiles, and partly due to a non-alibrated detetor response.
Fermi
is not strongly aeted by this eet sine the anti-oinidene shield was
designed in a segmented fashion [Moiseev
et al.
2007℄. The eetive area of
Fermi
is roughly an order of magnitude larger than that of EGRET leading to an inreased
sensitivity, see gure 1 of [Funk
et al.
2008℄.
This Chapter presents the general theory that up to day tries to explain the
diusion of osmi rays in the interestellar medium, ISM. In setion 2.2, possible
astrophysial senarios that were predited to be deteted at the high-energy end
of the observations with
Fermi
published in [Rodríguez Marrero
have been analyzed.
et al.
Those senarios have been
2008℄, previous to the
Fermi
launh, and are
thought to our as result of CR diusion in the ISM.
2.1 The role of diusion
When CR protons interat with ambient nulei, several types of partiles are produed. One of these produts are neutral pions,
gamma-ray photons.
π0,
whih naturally deay in two
Above hundreds of MeVs, the
π 0 -deay
gamma-ray emis-
sion dominates over bremsstrahlung and inverse Compton (IC) in the galati
plane [Fihtel
et al.
1976, Bertsh
a soure of proton-density
np
et al.
Z
∞
Eπmin
where
Fπ (Eπ ) = 4πnp
dσπ (Eπ , Ep )/dEπ
π 0 -deay
gamma-ray ux from
is
F (Eγ ) = 2
and
1993℄. The
Z
F (E )
p π π
dEπ ,
Eπ2 − m2π
Epmax
Epmin
Jp (E)
dσπ (Eπ , Ep )
dEp ,
dEπ
is the dierential ross-setion for the prodution of
[Domingo-Santamaría & Torres 2005, Kelner
(2.1)
et al.
(2.2)
π0,
e.g.,
2006℄. The limits of integration
in the last expression are obtained by kinemati onsiderations. Any possible gradient of CR or gas number density in the target has been impliitly negleted. The CR
2.1. The role of diusion
21
spetrum, whih is essentially mimiked by
π 0 -deay
gamma rays at high energies,
is given by:
cβ
Jp (E, r, t) =
f,
4π
where
r
(2.3)
f (E, r, t) is the distribution funtion of protons at an instant t and a distane
from the soure.
The distribution funtion
f
satises the radial-temporal-energy dependent dif-
fusion equation, [Ginzburg & Syrovatskii 1964℄, whih in the spherially symmetri
ase has the form:
D(E) ∂ 2 ∂f
∂
∂f
=
r
+
(P f ) + Q,
2
∂t
r ∂r ∂r
∂E
where
P = −dE/dt
is the energy loss rate of the partiles,
is the soure funtion, and
D(E)
(2.4)
Q = Q(E, r, t)
is the diusion oeient, for whih a depen-
dene only on the partile's energy is assumed.
The energy loss rate are due
to ionization and nulear interations, with the latter dominating over the for-
Pnuc = E/τpp , with
−1
(np c κ σpp ) being the timesale for the orresponding nulear loss, κ ∼ 0.45
mer for energies larger than 1 GeV. The nulear loss rate is
τpp =
being the inelastiity of the interation, and
σpp
being the ross setion (Gaisser
1990). [Aharonian & Atoyan 1996℄ presented a solution for the diusion equation
finj (E),
δ
suh that Q(E, r, t) = N0 finj (E)δr̄δ(t). For the partiular ase in whih D(E) ∝ E
−α , above 1 10 GeV, where the ross-setion to pp interations is a
and finj ∝ E
weak funtion of E , it reads
"
#
N0 E −α
(α − 1)t
R 2
f (E, r, t) ∼ 3/2 3 exp −
−
,
(2.5)
τpp
Rdif
π Rdif
with an arbitrary diusion oeient, and an impulsive injetion spetrum
where
Rdif = 2 D(E)t
exp( τtδpp ) − 1
tδ/τpp
!1/2
(2.6)
stands for the radius of the sphere up to whih the partiles of energy
to propagate after their injetion.
E
have time
In ase of ontinuous injetion of aelerated
Q(E, t) = Q0 E −α T (t), the previous solution needs to be onvolved with
′
′
funtion T (t − t ) in the time interval 0 ≤ t ≤ t [Atoyan et al. 1995℄.
R
N0 E −α
f (E, r, t) ∼
erf
,
(2.7)
4πD(E)R
Rdif (E, t)
partiles,
the
where
is the error funtion.
2
erf(z) =
π
Z
∞
exp(−x2 ) dx
(2.8)
z
In the following setion, typial values,
α = 2.2
and
δ = 0.5,
will be assumed.
22
Chapter 2. Diusion of osmi-rays
Figure 2.1: SEDs generated by CR propagation in ISM with dierent properties.
Fluxes orrespond to a loud with
M5 /d2kpc = 0.5.
Curve for
D10
= 10
26 , 1027 ,
28 m2 s−1 are shown with solid, dotted, and dashed lines respetively. Sen-
and 10
sitivities of EGRET (red) and
Fermi
(blue) (both for dierent diretions in the
sky with dierent bakground ontribution), H.E.S.S. (magenta) (survey mode and
pointed observations with typial integrations), and MAGIC (yellow), are shown for
omparison purposes (see gure 1 of [Funk
et al.
2008℄ for details on sensitivities).
2.2 Astrophysial senarios in the Pre-Fermi era
In the ase of energy-dependent propagation of CRs, a large variety of
γ -ray
spetra is expeted, e.g., [Aharonian & Atoyan 1996, Gabii & Aharonian 2007,
Torres
et al.
2008℄. This study presents systematially and numerially produed
more than 2000
E2F
distributions, and their dependenes with the involved pa-
rameters. Table 2.1 summarizes the results both for an impulsive and a ontinuous
aelerator.
The most surprising dependenes are related with the age of the a-
elerator and the diusion oeient, see Figure 2.1.
diret impat on the CR distribution.
These parameters have a
As the diusion inreases in speed, high
energy CR over larger distanes. The soure (loud) is parameterized in units of
M5 = MCl /105 M⊙
and
dkpc = d/
1 kp. The
ttransition
parameter, dened in the
ase of an impulsive aelerator, is the age for whih the timesale for the orresponding nulear loss beomes omparable to the age of the aelerator itself.
Dtransition
is the value of the diusion oeient for whih the SEDs stop displaing in energy
keeping approximately the same ux, as inferred from Figure 2.1.
Setting, as an example, reasonable parameters for the energy injeted by the
2.2. Astrophysial senarios in the Pre-Fermi era
Table 2.1:
Dependene of the SED (E
2 F vs.
E)
on various parameters.
23
Imp.
(ont.) stands for the impulsive (ontinuous) aelerator ase. Dependenes upon
loud parameters suh as density (nCl ), mass (MCl ), and radius (RCl ) are obvious
and related.
Parameter symbol and meaning
Eet on the E 2 F distributions versus E
Wp : total energy injeted as CRs
overall saling, small eets in the range
if in the typial range 1050 1051 erg
ont.: overall saling, small eets in the range
if in the typial range 1037 1038 erg s−1
imp.: peak displaes to smaller energies for a
xed distane, until t > ttransition , and the peak
displaes to smaller uxes
ont.: peak displaes to smaller energies and
larger uxes, for a xed distane
Aelerator
Lp : energy injeted per unit time
inreasing t: age of the aelerator
Interstellar medium
n: density
inreasing D10 :
diusion oeient of the medium
(at 10 GeV)
imp.:
negligible eets in the typial range 0.510 m−3,
sine τpp ≫ t.
for a xed age: displaement to smaller energies
until D10 > Dtransition where peaks generated
by louds at large separation, R, displae up
and peaks generated by louds at smaller R
displae down in the SED
for a xed distane: displaement to smaller
energies until D10 > Dtransition where peaks
generated by older aelerators (larger t)
displaes down and peaks generated by
younger aelerators (smaller t) displaes up
24
Chapter 2. Diusion of osmi-rays
Figure 2.2:
100 GeV
Examples of the model preditions for a hadroni maxima in the
regime.
1−
The left top (bottom) panel shows the preditions for a loud
M5 /d2kpc = 0.025 (0.04), loated at 20 (30) p from an aelerator of 104
4
27 m2 s− 1. The right top (bottom) panel
(3 × 10 ) yr, diusing with D10 = 10
2
urve shows the preditions for a loud saled at M5 /dkpc = 0.08 (0.06) loated at
3
4
28 m2 s− 1.
10 (20) p from an aelerator of 10 (10 ) yr, diusing with D10 = 10
2
Inreasing the ratio M5 /dkpc , the urves move up maintaining all other features.
saled at
Wp = 5×1049 erg for an impulsive soure and Lp =
37
−1
5 × 10 erg s for a ontinuous one) and for the interstellar medium density (e.g.,
n = 1 m−3 ), several senarios for the appearane of hadroni maxima produed by
aelerator into osmi-rays (e.g.,
diusion are found. Some examples are shown in Figure 2.2, for the two types of
aelerators. Two kinds of peaks at this energy regime are possible: those that are
not to be deteted by an instrument with the sensitivity of EGRET or MAGIC,
and those that are not to be deteted by an instrument like H.E.S.S. or VERITAS.
The impulsive aelerator produes a more narrow peak maxima. A maxima in the
SED, hadronially produed as an eet of diusion of CRs, is possible and not
unommon at the high-energy end, where they produe a level of ux detetable by
Fermi
LAT.
Figure 2.3 displays, as ontour plots, the energy at whih the maximum of the
SED is found for the ases of impulsive aeleration of osmi rays, at dierent distanes, ages of the aelerator, and diusion oeients. The impat of the diusion
is learly shown by this gure, whih hanges are due to pure energy-dependent propagation eets. The diusion radius, for
t ≪ τpp ,
is
p
Rdif (E) = 2 D(E)t,
so that at
a xed age and distane, only partiles of higher energy will be able to ompensate a
2.2. Astrophysial senarios in the Pre-Fermi era
smaller
D10 ,
25
E -values. The smaller values of D10
[Ormes et al. 1988, Torres et al. 2008℄.
produing SED maxima at higher
are expeted in dense regions of ISM, e.g.,
It is interesting to note that for many, albeit not for all, of the SEDs studied, the
maximum is found at energies beyond the
Figure 2.3 interpretes a
Fermi
Fermi
aeptane. On the other hand,
observational disovery of a
1 − 100 GeV
maximum,
and provides interesting lues about the nature of the astrophysial system that
generates the gamma rays. First, these SEDs are found in ases where the senario
does not predit detetable emission at the EGRET sensitivity, so that they will
represent new phenomenology. Seond, the range of aelerator-target separations
and ages of the aelerator that would produe suh a
1 − 100
GeV maximum is
rather limited (see in Figure 2.3 the narrow ontours for maxima at suh energies).
This would lead to a diret identiation of the soure.
Another interesting possibility is the ase of two unresolved soures. Two separate aelerator-loud omplexes are onsidered lose to the line of sight, suh that
they would be observed as a single soure.
an inverted spetrum.
This kind of senarios would produe
Figure 2.4 shows four possible inverted spetra.
The two
gures in the top (bottom) panel are generated by an impulsive (ontinuous) aelerator. The SED reated by the oldest (youngest) aelerator is shown by dashed
(dot-dashed) lines in eah of the senarios. For the left ases, EGRET should have
been able to weakly detet the soure produing uxes at smallest energies. In any
ase, EGRET ould not onlusively relate it to suh phenomenon due to its large
low-energy PSF. The ounterpart at higher energies is a bright soure potentially
detetable by ground-based telesopes. Due to ontinuous energy overage,
Fermi
is
a prime instrument to trak this phenomenology, although none has been reported
up to now. The right panel ases show partiular examples in whih the detetion
of the soure by an instrument with the sensitivity of EGRET is not possible at all.
The inverted spetrum is less deep in these senarios. Less pronouned V-shaped
spetra an be obtained with onomitantly lower uxes at TeV energies.
2.2.1 Disussion
Compton
peaks
[Aharonian
et al.
(whih
rst
example
ould
have
been
found
already,
2006℄) are not the only way to generate a maximum in a SED. A
large variety of parameters representing physial onditions in the viinity of a CR
aelerator ould produe a rather similar eet. Distinguishing between these ases
would require multiwavelength information, searh for ounterparts, and modelling.
If suh a maximum is interpreted hadronially, as a result of diusion of CR in the
ISM and their subsequent interation with a nearby target, the results presented
herein onstrain, given the energy at whih the maximum of the SED is reahed,
the harateristis of the putative aelerator, helping to the identiation proess.
Indeed, one of the most distinguishing aspets of this study is the realization that
these signatures (in partiular, peaks at the
1 − 100 GeV energy region)
is indiative
for an identiation of the underlying mehanism produing the gamma rays that
ours in nature: whih aelerator (age and relative position to the target loud)
26
Figure 2.3:
Chapter 2. Diusion of osmi-rays
For eah ombination of age and aelerator-target separation, for
whih more than two thousand spetra where numerially produed, the energy of
the maximum of suh spetra are shown in a ontour plot. The olor of the dierent
ontours orresponds to the range of energy where the maximum is found aording
to the olor bar above eah gure. From top to bottom, plots are reated for the
ase of an impulsive soure injeting protons in a medium with
1027 m2 s−1
and
1028 m2 s−1 .
D10 =1026 m2 s−1 ,
2.2. Astrophysial senarios in the Pre-Fermi era
Figure 2.4:
27
The parameters for the plots are as follows, (top left) the dashed urve
t = 4×105 yr, R = 5 p, M5 /d2kpc = 0.01; the dashed urve on the right:
t = 104 yr, R = 20 p, M5 /d2kpc = 0.1; (top right) the dashed urve on the left: t =
6
3
2
2×10 yr, R=100 p, M5 /dkpc = 3; the dashed urve on the right: t = 4×10 yr, R
2
6
= 15 p,M5 /dkpc = 0.1; (bottom left) the dashed urve on the left: t = 2×10 yr,
2
3
R=15 p, M5 /dkpc = 0.004; the dashed urve on the right: t = 10 yr, R = 5 p,
M5 /d2kpc = 1; ( bottom right) the dashed urve on the left: t = 2×106 yr, R = 40 p,
M5 /d2kpc = 0.017; the dashed urve on the right: t = 6×104 yr, R = 30 p,M5 /d2kpc
26 m2 s−1 . R is the aelerator-loud separation.
= 2.5. D10 is set to 10
on the left:
28
Chapter 2. Diusion of osmi-rays
and under whih diusion properties CR propagate, as it is exemplied in Figure
2.3. In a survey mode suh as the one
Fermi
LAT performs, it is also possible to nd
rather unexpeted, tell-tailing SEDs, like those V-shaped presented here, if observed
with instruments having a limited PSF, preditably leaving many Galati soures
unresolved.
2.3 Moleular louds illuminated by CRs from SNRs
Non-thermal emission is expeted to ome from moleular louds,
terations of CR that penetrate the loud.
whenever the moleular loud is in the proximity of a SNR [Gabii
[Rodríguez Marrero
et al.
due to in-
This emission would be enhaned
et al.
2009℄,
2009℄. The moleular louds provide a dense target for the
CR that esape and subsequently diuse away from the aelerator (i.e., the SNR).
When both soures of CR are lose with respet to the line of sight, a onave spetrum appears in gamma rays, reeting the shape of the underlying CRs. This alternative V-shaped spetrum of CRs was thouroghly studied in [Gabii
et al.
2009℄.
A hadroni senario, where gamma rays mainly appear as a result of neutral
pion deay produed in
pp
interations, would be favoured if spatial orrelation
were found between TeV gamma rays and dense gas.
A moleular loud, sit-
uated lose to a SNR, would appear illuminated by the CR esaping the SNR
and produe gamma rays. This assoiation was already presented as the possible
soure of unidentied TeV soures deteted by ground based Cherenkov telesopes
[Gabii & Aharonian 2007℄. The model explored in [Gabii
et al.
2009℄ inludes not
only the hadronially produed photons, but also the seondary eletrons generated
in the loud, together with the bremsstrahlung and IC emission. The diusion oeient inside the loud is assumed to be similar to the Galati one, in order to
have a free penetration of the CRs.
The total CR spetrum onsidered therein has two ontributions: one oming
from the Galati bakground and the other from the CRs that esape the aelerator.
The rst ontribution is haraterized by a steep spetrum that peaks in
the GeV energy region, and it is not supposed to hange with time. On the other
hand, the runaway CRs will be variable in time and their spetrum is hard. At the
highest energies, in the TeV range, this seond peak dereases and moves to lower
energies. This eet omes from the fat that CRs diuse earlier and faster away
from the aelerator at PeV energies than at lower energies (GeVs, TeVs). Taking
into aount both ontributions, the CR spetrum aquires a onave shape, whih
is reeted in gamma rays. The aoredmentioned evolution in time is proportional
to the square of the separation between the moleular loud and the SNR. The CR
spetrum presents a ut-o, whih position depends on the last partiles with energy
enough that have time to reah the loud.
The detetion of suh a shape ould prove the presene of a CR aelerator
lose to moleular louds, and maybe larify the nature of up-to-now unidentied
TeV soures.
One possibility to ahieve this goal would be overing the whole
2.3. Moleular louds illuminated by CRs from SNRs
energy range with joint observations of
Fermi
29
and the next generation of ground
based Cherenkov telesopes (CTA). An initial study on this diretion is explored in
Chapter 8.
Chapter 3
Appliations to the environment
of SNR IC443: Pre-Fermi study
Contents
3.1 IC443 plaed into ontext . . . . . . . . . . . . . . . . . . . . 31
3.2 MAGIC and EGRET observations of the region . . . . . . . 34
3.3 A model for MAGIC J0616+225 . . . . . . . . . . . . . . . . 35
3.3.1
Results of the model . . . . . . . . . . . . . . . . . . . . . . .
35
3.4 Disussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Of all supernova remnants (SNRs) that were found to be positionally oinident
with gamma-ray soures in the MeV range in the EGRET era, IC 443 was one of
the most appealing for subsequent observations with higher sensitivity instruments
(see the ase-by-ase study by [Torres
et al.
2003℄). It was, together with W28, the
only ase in whih the moleular environment - as mapped for instane with CO
observations - showed a peak in density lose by, but separated in sky projetion,
This would allow distinguishing
from the SNR enter, as shown in Figure 3.1.
possible osmi-ray (CR) diusion eets, in ase the gamma-ray emission observed
would be hadronially produed.
Several observations of the IC 443 environment
have been made at the highest energies, and in this Chapter, these are used in the
setting of a theoretial model in whih CRs from the SNR IC 443 are diusing away
from it and interating with louds nearby. This model has been originally presented
in [Torres
et al.
2008℄.
3.1 IC443 plaed into ontext
IC
443
is
an
asymmetri
[Fesen & Kirshner 1980℄).
shell-type
SNR
with
evidene
ages,
e.g.
[Rho
for
et al.
a
diameter
multiple
2001℄.
dense
In radio,
et al.
lumps,
1990℄.
is
also
[Hewitt
et al.
2006℄
onrmed
The interation reseen
in
2MASS
im-
these
et al. 1997℄ re(l, b) ∼ (−171.0, 2.9).
[Claussen
ported the presene of maser emission at 1720 MHz at
on,
(e.g.,
IC 443 has a spetral index of 0.36,
and a ux density of 160 Jy at 1 GHz [Green 2004℄.
Later
∼45'
of
Two half shells appear in optial and radio images,
e.g, [Braun & Strom 1986, Leahy 2004, Lasker
gion,
with
measurements
and
disovered
32
Chapter 3. Pre-Fermi study on the environment of SNR IC443
Figure 3.1:
CO distribution around the remnant IC 443 (G189.1+3.0). The 3EG
gamma-ray soure J0617+2238 is plotted with white ontours. The optial boundary
of the SNR is superimposed as a blak ontour [Lasker
et al.
1990℄.
emission seems to fade in regions where CO emission inreases.
The optial
This indiates
that the moleular material is likely loated on the foreground side of the remnant,
absorbing the optial radiation. Plot taken from [Torres
et al.
2003℄, gure 10.
3.1. IC443 plaed into ontext
weaker
nent
maser
X-ray
soures
soure,
et al.
[Keohane
in
observed
1997℄,
XMM
Bohino & Bykov 2003,
[Olbert
[Bykov
et al. 2001,
et al. 2008℄
the
33
region
with
of
Rosat
interation.
a
promi-
[Asaoka & Ashenbah 1994℄,
ASCA
[Bohino & Bykov 2000,
IC
Gaensler
is
Bohino & Bykov 2001,
et al. 2005, Troja et al.
et al. 2006℄. The works by
Bykov
summarize these observations.
443
2006℄,
[Troja
and
Chandra
et al.
2006℄ and
Some additional features of
IC 443 are presented next, due to their relevane for the model.
Age
et al. 1992℄ and seonded
Ashenbah 1994℄ and [Keohane et al. 1997℄, although IC 443
4
to have a middle-age of about 3 × 10 yrs. This age has been
A small (∼ 1000 yr) age was determined by [Wang
by [Asaoka &
is now agreed
initially advoated by [Lozinskaya 1981℄ and was later onsistently obtained
as a result of the SNR evolution model [Chevalier 1999℄.
[Bykov
et al.
Observations by
2008℄ onrm that there are a few X-ray-emitting ejeta frag-
ments, a number muh smaller than that expeted for a younger SNR.
Distane
Kinematial distanes from optial systemi veloities span from 0.7 to 1.5 kp,
e.g., [Lozinskaya 1981℄.
The assumption that the SNR is assoiated with
∼ 1.5 − 2.0 kp.
a nearby HII region, S249, implies a distane of
Sev-
eral authors laimed that the photometri distane is more reliable, e.g,
[Rosado
et al.
2007℄, and onurrently with all other works on IC 443, a dis-
tane of 1.5 kp is adopted here (thus, 1 armin orresponds to 0.44 p).
Energy of the explosion
E51 , a term dened as the energy of the explosion
50 erg,
[Chevalier 1999℄ obtains a lower limit of 4 × 10
lower estimations are provided by [Dikman et al. 1992℄, based on
et al. 1986℄, albeit the latter assumed an age of ∼5000 yr. Laking
There is no lear indiator for
51 erg.
in units of 10
whereas
[Mufson
a strong reason for other numerial assumptions, in the following model it
will be assumed
E51 = 1,
although to be onservative, it will subsequently
be assumed that only 5% of this energy is onverted into relativisti CRs.
Reasonable dierenes in this assumed value of
E51
are not expeted to have
any impat on the model.
The moleular environment
[Cornett
to
et al.
present
Later
on,
1977℄ and [De Noyer & Frerking 1981℄ were among the rst
detailed
[Dikman
et al.
observations
et al.
1992℄,
of
[Seta
moleular
et al.
lines
1998℄,
towards
[Butt
et al.
IC
2003℄
443.
and
2003℄ among others, presented further analysis.
These works
onform the urrent piture for the environment of IC 443:
a total mass
[Torres
of
∼ 1.1 × 104
M⊙ mainly loated in a quiesent loud in front of the
remnant (with linear sales of a few parses and densities of a few hun-
−3 ) that is absorbing optial and X-ray radiation, e.g.,
dred partiles m
Chapter 3. Pre-Fermi study on the environment of SNR IC443
34
et al. 1990, Troja et al. 2006℄, a senario already put forward
[Cornett et al. 1977℄. [Dikman et al. 1992℄ estimated that 500 − 2000 M⊙
[Lasker
by
are
diretly perturbed by the shok in the northern region of interation, near the
SNR itself.
[Huang
et al.
1986℄ found several lumps of moleular material
along this interating shell, with subparse linear sales. [Rosado
et al.
2007℄
found inhomogeneities down to 0.007 p. As a rst approximation to the problem, these latter inhomogeneities are negleted when onsidering the propagation of CRs in the ISM, i.e. it is assumed an homogeneous medium of typial
ISM density where CRs diuse. Then, the moleular mass senario is a main
giant loud in front of the SNR ontaining most of the quiesent moleular
material found in the region, and smaller loud(s) totalizing the remaining
mass loated loser to the SNR.
3.2 MAGIC and EGRET observations of the region
The rst gamma-ray emission oming from the SNR IC 443 was labeled as
the EGRET soure 3EG J0617+2238 [Hartman
et al.
1999℄.
The EGRET ux
−8 ph m−2 s−1 , with a photon spetral index of 2.01 ± 0.06
was (51.4 ± 3.5) ×10
et al. 1999℄. The EGRET soure was lassied as non-variable by
et al. 2001a, Nolan et al. 2003℄. An independent analysis of GeV pho-
[Hartman
[Torres
tons
measured
by
EGRET
ended
up
being
the
soure
GeV
J0617+2237
[Lamb & Maomb 1997℄, also at the same loation of 3EG J0617+2238 at the enter
of the SNR.
Later
on,
MAGIC
observations
towards
IC
443
yielded
the
detetion
of
J0616+225 nearby, but displaed from the enter of the SNR IC 443, with en-
h
m 43s , +22◦ 31' 48),
troid loated at (RA,DEC)J2000 =(06 16
[Albert
et al.
± 0.025◦stat ± 0.017◦sys
2007b℄. The MAGIC Collaboration showed that the very high energy
(VHE) soure is loated at the position of a giant loud right in front of the SNR.
A simple power law was tted to the measured spetral points:
dNγ
dAdtdE
= (1.0 ± 0.2stat ± 0.35sys ) × 10−11
−3.1±0.3stat ±0.2sys
E
cm−2 s−1 TeV−1
0.4TeV
(3.1)
with quoted errors being statistial. The systemati error was estimated to be 35%
in ux and 0.2 in spetral index.
The integral ux of MAGIC J0616+225 above
100 GeV is about 6.5% of the Crab Nebula.
observation time (over one year).
No variability was found along the
No signiant tails or extended struture was
found at the MAGIC angular resolution. These results were onrmed by observations with the VERITAS array [Humensky & the VERITAS Collaboration 2008℄.
dNγ /(dAdt) <
−12
−2
−1
6 × 10 cm s
(0.11 Crab) above 500 GeV [Holder et al. 2005℄ and by CAT
dNγ /(dAdt) < 9 × 10−12 cm−2 s−1 above 250 GeV [Kheli 2003℄.
In addition, onsistent upper limits were reported by Whipple
3.3. A model for MAGIC J0616+225
35
MAGIC J0616+225 is displaed with respet to the position of the lower energy
soure 3EG J0617+2238.
Indeed, the EGRET entral position is loated diretly
towards the SNR, whereas the MAGIC soure is south of it, lose to the 95% CL
ontour of the EGRET detetion.
As [Albert
et al.
2007b℄ showed, the MAGIC
soure is loated at the position of a giant loud in front of the SNR. The aim of the
model presented here is to show evidene of them being related. Extrapolating the
spetrum of the EGRET soure into the VHE regime, a higher ux and a harder
spetrum than the one observed for MAGIC J0616+225 would be obtained, supporting the view that a diret extrapolation of this and other EGRET measurements
into the VHE range is not valid [Funk
et al.
2008℄.
3.3 A model for MAGIC J0616+225
A theoretial model is presented in this Chapter and the previous one, explaining the high energy phenomenology of IC 443 (see [Aharonian & Atoyan 1996,
plaing an emphasis on the displaement between
Gabii & Aharonian 2007℄),
EGRET and MAGIC soures. MAGIC J0616+225 is interpreted as a delayed TeV
emission of CRs diusing from the SNR. This model is ompared with other ontemporary studies, together with a disussion on how it an be tested using observations
with the
Fermi -LAT
instrument (at that time still to ome).
The model [Torres
et al.
2008℄ is based on the senario of CR diusion, as de-
sribed in the previous Chapter.
this spei soure.
The parameters have been adjusted here for
CRs are aelerated at the SNR site and end up interat-
ing with the nulei present in the interestellar medium (ISM), produing a set of
partiles, inluding both harged and neutral pions.
through
π0 −deay.
Gamma rays are generated
The CR spetrum of the protons is given by a distribution
funtion that satises the radial-temporal-energy dependent diusion equation of
[Ginzburg & Syrovatskii 1964℄. Details on this issue are given in Chapter 2. Two
assumptions are onsidered: a diusion oeient dependent only on the energy,
E −δ , and a power-law for the distribution funtion of the injeted proton
−α ). Both impulsive and ontinuous injetion of CR protons from the
spetrum (∝ E
D(E) ∝
aelerator are onsidered (equations 2.5 and 2.7) in the following results. Finally,
α = 2.2
is assumed.
3.3.1 Results of the model
Figure 3.2 shows the urrent CR spetrum generated by IC 443 at two dierent
distanes from the aelerator, 10 (solid) and 30 (dashed) p. The SNR is onsidered both as a ontinuous and an impulsive aelerator. In the ontinuous ase, a
relativisti proton power of
Lp = 5 × 1037 erg s−1
is assumed, and the proton lumi-
nosity is suh that the energy injeted into relativisti CRs through the SNR age is
5 × 1049
erg. If an impulsive injetor is onsidered, then it has the same total power
but the injetion of high energy partiles our in a muh shorter timesale than
the SNR age. The horizontal line in Figure 3.2 marks the CR spetrum near Earth,
36
Chapter 3. Pre-Fermi study on the environment of SNR IC443
Figure 3.2: CR spetrum generated by IC 443 at two dierent distanes, 10 (solid)
and 30 (dashed) p, at the age of the SNR. Two types of aelerator are onsidered,
one providing a ontinuous injetion (blak) and other providing a more impulsive
injetion of CRs (red). The horizontal line marks the CR spetrum near the Earth.
The Y-axis units have been hosen to emphasize the exess of CRs in the SNR
environment.
so that the exess of CRs in the SNR environment an be seen. For this ase, the
diusion oeient at 10 GeV,
D10 ,
was hosen to be 10
26 m2 s−1 , with
δ = 0.5.
CRs propagate through the ISM, whih is assumed to have a typial density, e.g.
nISM = 0.5, 1, 5,
and 10 m
−3 . In the sale of Figure 3.2, urves for this set of
values would be superimposed, so that
nISM
beomes an irrelevant parameter in
this range. The reason for this is that the timesale for nulear loss
τpp ,
obtained
with the densities onsidered for the ISM, is orders of magnitude larger than the age
of the aelerator.
Dierenes between the dierent kind of aelerators assumed
are also minimal for the SNR parameters.
Figure 3.3 shows the result for the gamma-ray emission oming from the loud
loated at the position of the MAGIC soure, when it is assumed that the soure
lies at dierent distanes in front of IC 443.
The giant loud mass is assumed
(onsistently with observations) to be 8000 M⊙ .
The aelerator properties and
power of IC 443 are those shown in Figure 3.2, for eah ase. Fluxes are given for
an ISM propagation in a medium of
n = 1 m−3 ,
although this is not a relevant
parameter, as it has been disussed beforehand. Clouds loated from
produe an aeptable math to MAGIC data.
∼20 to ∼30 p
In the ase of a more impulsive
aelerator, the VHE predited spetra is slightly steeper than that produed in
the ontinuous ase at the same distane, providing a orrespondingly better t to
the MAGIC spetrum.
Figure 3.3 also shows, apart from MAGIC data, EGRET
measurements of the neighborhood of IC 443. As it has been stated previously, these
two soures are not loated at the same plae, highlighted with dierent symbols in
3.4. Disussion
37
the plot. Figure 3.3 shows that there is plenty of room for a loud the size of the
one deteted in front of IC 443 to generate the MAGIC soure and not a o-spatial
EGRET detetion.
The existene of a VHE soure without a ounterpart at lower energies is the
result of diusion of the high-energy CRs from the SNR shok, whih is an energy
dependent proess leading to an inreasing deit of low energy protons as the
distane from the aelerator beomes larger.
To larify this assertion, and sine
the solution to the diusion-loss equation is a funtion of time, the evolution of the
ux along the age of the SNR is shown in Figure 3.4. The integrated photon ux
oming from the position of the giant loud is presented as a funtion of time above
100 MeV and 100 GeV in the impulsive ase. Dierent qualities of the aelerator
(impulsive or ontinuous) produe a rather omparable piture. At the age of the
SNR,
Fermi
is predited to see a soure only for the losest separations.
On the
ontrary, the integrated photon uxes above 100 GeV present minimal deviations,
and a MAGIC soure is always expeted.
Figure 3.3 also presents the results of this theoretial model fousing in the
energy range of EGRET. At these low energies, the CR spetrum interating with
a loal-to-the-SNR loud is obtained assuming an average distane of interation
of
3 − 4 p.
A few hundred M⊙ loated at this distane (∼700 M⊙ in the ase of
an impulsive, and
∼300 M⊙
for a ontinuous ase) produe an exellent math to
the EGRET data, without generating a o-spatial MAGIC soure. As defended in
[Gaisser
et al.
1998℄, the lowest energy data points in the EGRET range (below 100
MeV) are produed by bremsstrahlung of aelerated eletrons.
The present model imposes some onstraints provided by the observed phenomenology, like e.g., the moleular environment and the position of the gammaOne of the onsequenes is that D10 should be low, of the order of
26
2
−1
28 m2 s−1 . By
10 m s
, whereas the harateristi value on the Galaxy is ∼10
ray soures.
varying the diusion oeient, its inuene in the results an be studied. If the
> 10
separation between the giant loud and the SNR is
(D10
p, a slower diusion
26 m2 s−1 ) would not allow suient high energy partiles to reah the
>
10
target material; thus, the MAGIC soure would not be there. On the other hand, if
the separation between the main loud and the SNR is
< 10 p,
the EGRET soure
would have been deteted at the position of the loud, whih is not the ase. The
value of
D10
established in this study, at 1.5 kp from Earth, has been dened by
ombining MAGIC and EGRET observations. Suh low values of
in dense regions of ISM [Ormes
et al.
D10
are expeted
1988, Gabii & Aharonian 2007℄.
3.4 Disussion
In
this
[Bykov
setion,
et al.
the
disussed
model
is
plaed
in
the
ontext
of
others.
2000℄ suggested that the GeV emission seen towards IC 443 is mostly
due to relativisti bremsstrahlung. As noted by [Butt
et al.
2003℄, who already favor
a hadroni emission of gamma-rays, the synhrotron radio emission seen towards the
38
Chapter 3. Pre-Fermi study on the environment of SNR IC443
Figure 3.3:
MAGIC and EGRET measurement of the neighborhood of IC 443 (stars
and squares, respetively) as ompared with model preditions. The top (bottom)
panel shows the results for an impulsive (ontinuous) ase. At the MAGIC energy
range, the top panel urves show the preditions for a loud of 8000 M⊙ loated
at 20 (1), 25 (2), and 30 (3) p, whereas they orrespond to 15 (1), 20 (2), 25
(3), and 30 (4) p in the bottom panel.
At lower energies, the urve shows the
predition for a few hundred M⊙ loated at
3 − 4 p.
The EGRET sensitivity
urves (in red) are shown for the whole lifetime of the mission for the Galati
anti-entre (solid), whih reeived the largest exposure time and has a lower level of
diuse gamma-ray emission, and for a typial position in the Inner Galaxy (dashed),
more dominated by diuse gamma-ray bakground.
The
Fermi
sensitivity urves
(in blue) show the simulated 1-year sky-survey sensitivity for the Galati North
pole, whih orresponds to a position with low diuse emission (solid), and for
a typial position in the Inner Galaxy (dashed).
These urves were taken from
http://www-glast.sla.stanford.edu/software/IS/glast_latperformane.html.
[Rodríguez Marrero
et al.
2009℄.
From
3.4. Disussion
39
Figure 3.4: Integrated photon ux as a funtion of time above 100 MeV and 100 GeV,
solid (dashed) lines orrespond to the ase of the loud loated at 10 (30) p. The
horizontal lines represent the values of integrated uxes in the ase that the CR
spetrum interating with the loud is the one found near Earth.
line stands for the SNR age.
EGRET and
Fermi
The vertial
initially predited integral
sensitivity are shown, onsistent in value and olor oding with those in Figure 3.3.
rim of the SNR and the entrally loated EGRET soure must then be assoiated.
Judging from the loalization of the multiwavelength emissions, this does not seem
to be the ase. An unavoidable (but subdominant at high energies) bremsstrahlung
omponent oming from primary and seondary eletrons an however play a role at
the lowest energies in the EGRET range, as already shown by [Gaisser
et al.
1998℄
and Figure 3.3.
[Bohino & Bykov 2001℄ suggested that the systemati errors in the EGRET
loation ontours ould yield the pulsar CXOU J061705.3+222127 disovered by
[Olbert
et al.
2001℄ and its nebula, as the soure of the GeV emission. As disussed
above, this ontradits urrent observations. The same assumption (i.e., that the
positions of the measured EGRET and GeV soures are wrong by half a degree)
was taken by [Bartko & Bednarek 2008℄. The pulsar nebula is also displaed from
the MAGIC detetion by 20 armin, but these authors suggested that they may be
onneted if a pulsar with a veloity of 250 km s
−1 moves along the SNR age. This
implies that the pulsar CXOU J061705.3+222127 should have been born at the SNR
enter and should have traveled to its urrent position while aelerating partiles
that interat with the loud, giving rise to the MAGIC soure. This senario does
not seem to math the observed phenomenology: the EGRET soure should be on
top of the urrent position of the pulsar and not where it atually is, and physially,
it should be the result of pulsed emission (like in Vela), although pulses were not
reported during the EGRET era. The only argument supporting the latter assumption is that the ux and spetrum of 3EG J0617+2238 are similar to that of PSR
Chapter 3. Pre-Fermi study on the environment of SNR IC443
40
1706-44, also observed by EGRET. This would apply to dozens of other EGRET
soures but an not be sustained as irumstantial evidene of physial similarity, e.g., [Romero
et al.
1999, Reimer 2001, Torres
et al.
2001b, Torres
et al.
2003℄.
Still within the same senario, the MAGIC soure is onsidered to be generated by
inverse Compton from eletrons aelerated at an initial phase of the pulsar and
travelling towards the loud.
The loalization and size of the MAGIC soure are
not explained sine the dierene in target photon elds in the region surrounding
the loud should not be signiant, and the target eld should even be larger at the
position of the interating shok in the northeast.
[Zhang & Fang 2008℄ presented an alternative model for IC 443, in whih a fration of the SNR shell evolves in the moleular loud, and other in the ambient
interstellar environment, enountering dierent matter densities. In this model, the
gamma-rays observed by EGRET are mainly produed via
pp
interations with the
ambient matter in the louds, similar to that found in the MAGIC soure. Although
this may sound similar to the present model, there is a key dierene between them:
in Zhang and Fang senario, both EGRET and MAGIC soures should be at the
same position. The reason for this lies in the fat that, in their model, the radial
dependene of the CR spetrum is not onsidered. [Gabii & Aharonian 2007℄ noted
in general that an old SNR annot onne multi-TeV partiles in their shells, as it
has also been shown in the IC 443 results of this Chapter.
3.5 Summary
In this Chapter, MAGIC J0616+225 is found to be onsistent with the interpretation of CR interations with a giant moleular loud lying in front of the remnant,
produing no ounterpart at lower energies. Moreover, the nearby EGRET soure
an be explained as produed by the same aelerator, and in this ase, a o-spatial
MAGIC soure is not expeted.
In the present model, the displaement between
EGRET and MAGIC soures has a physial origin. It is generated by the dierent
properties of the proton spetrum at dierent loations, in turn produed by the
diusion of CRs from the aelerator (IC 443) to the target.
At high energies, a morphologial and spetral hange should ome from the
position of the loud (i.e. the enter of MAGIC J0616+225) towards the enter of
IC 443. At a morphologial level, the lower the energy, the more oinident with the
SNR the radiation will be deteted. At a spetral level, suient statistis should
show that the lower the gamma-ray energy the harder the spetrum is. In addition,
Fermi
LAT measurements are predited to be sensitive enough to detet the same
loud that shines at higher energy.
All these preditions will be disussed in the following Chapter, ombining the
MAGIC stand-alone data with the new observations by
Fermi
and AGILE at HE,
and by VERITAS at VHE. Related to this topi, preliminar observations made with
the MAGIC stereo system at VHE will be presented in Chapter 9, together with
prospets on the forthoming Cherenkov Telesope Array (CTA).
Chapter 4
The GeV to TeV onnetion in
SNR IC 443
Contents
4.1 New high and very high-energy observations . . . . . . . . . 41
4.2
4.3
4.4
4.5
4.1.1
Relative loalization of soures . . . . . . . . . . . . . . . . .
4.1.2
Possible relationship between gamma-ray emission and the PWN 43
.
.
.
.
43
45
46
49
4.5.1
Inuene of the δ -parameter . . . . . . . . . . . . . . . . . . .
50
4.5.2
Unertainties due to the ross setion parameterization . . .
51
Comparison with nominal model . . . . . . . . . . . . .
Using Fermi LAT data to onstrain model parameters
Cosmi-ray distributions and their eets . . . . . . . .
Degeneraies and unertainties . . . . . . . . . . . . . .
.
.
.
.
.
.
.
.
42
4.6 Computation of seondaries other than photons . . . . . . . 54
4.7 Conluding remarks . . . . . . . . . . . . . . . . . . . . . . . . 55
In the previous Chapter 3, the soure MAGIC J0616+225 has been interpreted
as a result of delayed TeV emission of osmi rays (CR) diusing from the supernova remnant (SNR) IC 443 and interating with a loud in the foreground of the
remnant. This model was used to make preditions for observations with the
satellite. Reently, AGILE,
Fermi
Fermi
LAT, and VERITAS released new results from
their observations of IC 443. In this Chapter, those results are ompared with the
preditions of the model, exploring the GeV to TeV onnetion in this region.
Fermi
LAT data is used to onsider the possibility of onstraining the osmi-ray diusion
features of the environment. Moreover, the osmi-ray distributions, their interations, and a possible detetion of the SNR environment in the neutrino hannel are
analyzed. The study presented here was published as [Torres
et al.
2010℄.
4.1 New high and very high-energy observations
Reently, the Very Energeti Radiation Imaging Telesope Array System (VERITAS) presented further observations towards IC 443 [Aiari
et al.
2009b℄.
Re-
garding the position of the entroid, it was found to be at (RA, DEC)J2000 =
h
m 51s , +22◦ 30' 11),
(06 16
± 0.03◦stat ± 0.08◦sys
thus, onsistent with that of MAGIC.
42
Chapter 4. The GeV to TeV onnetion in SNR IC 443
E > 100 GeV) extended gamma-ray emis◦
◦
◦
sion was also found. The extension derived was 0.16 ± 0.03stat ± 0.04sys . The
−Γ ) with
VHE spetrum was well t by a power law (dN/dE = N0 × (E/TeV )
a photon index of 2.99 ± 0.38stat ± 0.3sys and an integral ux above 300 GeV of
(4.63 ± 0.90stat ± 0.93sys ) × 10−12 m−2 s−1 . Thus, the spetral determination is
Evidene of a very-high-energy (VHE,
onsistent with the MAGIC measurements; both present a steep slope, with VERITAS nding a slight overall inrease in the ux level. No variability of the gamma-ray
emission was laimed by VERITAS either.
Moreover,
[Tavani
et al.
AGILE
2010℄.
results
on
IC
443
has
been
reently
reported
AGILE disovered a distint pattern of diuse emission
in the energy range 100 MeV3 GeV oming from the SNR, with a prominent
maximum loalized in the Northeastern shell, displaed (as it was the ase with
EGRET) respet to the MAGIC/VERITAS soures.
∼0.4o
The latter are
apart
from the maximum of the AGILE emission (whih is also separated from the
position of the nearby pulsar wind nebula (PWN), as disussed below).
Fermi
Finally,
has also reently presented an analysis of its rst 11 months of observations
towards the region of SNR IC 443 [Abdo
et al.
2010g℄. These results reinfore those
obtained by AGILE, given the better instrument sensitivity. Therefore,
Fermi
LAT
measurements will be preferably used when analyzing GeV results in this Chapter.
The soure has been deteted in a broad range of energies, from 200 MeV up to
50 GeV, with a SED that rolls over at about 3 GeV to seemingly math in slope
that found at the highest energies. The spetrum an be represented, for instane,
with a broken power law with slopes of 1.93
at
3.25 ± 0.6 GeV.
± 0.03
and 2.56
± 0.11,
with a break
This is one important dierene with the previously disussed
EGRET data. The spetral energy distribution (SED) ould not unveil bak then
neither that the emission would maintain a hard spetrum up to suh tens-of-GeV
energies, nor the existene of a roll over in the spetrum at the energies found. The
ux above 200 MeV resulted in (28.5±0.7)
very signiant detetion in
Fermi.
×10−8 ph m−2 s−1 ,
thus allowing for a
The entroid of the emission is onsistent with
that of EGRET 3EG J0617+2238.
4.1.1 Relative loalization of soures
et al. 2010g℄ report that the entroid of the Fermi LAT emission is displaed
error (MAGIC error) from that of MAGIC (J0610+225), and more
5 × θ68
error (VERITAS error) from that of the VERITAS soure. These num1.5 × θ68
[Abdo
more than
than
bers are obtained assuming that the systemati and statistial errors in loalization
add up in quadrature, and onsidering the worse error of eah of the pairs of measurements (Fermi MAGIC,
Fermi VERITAS),
whih in both ases orrespond to
the imaging air Cherenkov telesopes (IACTs). The signiane of the entroid separation greatly improves when a) the best measured position is onsidered (i.e., the
error by
Fermi
LAT), for whih both pairs of measurements are about 5σ away,
and/or b) when only statistial errors are onsidered for VERITAS (the systemati
errors in this latter measurement is about a fator of 3 larger than the statistis
4.2. Comparison with nominal model
43
and signiantly dierent from all others; but of ourse, one an not neessarily assume it to approah the detetion in the diretion of the
Fermi
LAT soure). Thus,
albeit urrent measurements are not onlusive about energy dependent morphology, they are onsistent with it. [Abdo
Fermi
et al.
2010g℄ report that the entroid of the
LAT emission moves towards that of the VERITAS soure as the energy band
1 − 5 GeV to 5 − 50 GeV. However, the signiane of this displaeonly ∼ 1.5σ . It might be that the angular resolution and/or sensitivity
hanges from
ment is low:
and/or the separation of the real moleular mass distribution on sky projetion are
not enough to distinguish when suh nearby energy ranges are onsidered.
New
measurements from MAGIC (using the just-obtained stereosopi apability) ould
provide ontinuous overage from 50 GeV up.
4.1.2 Possible relationship between gamma-ray emission and the
PWN
In all energy bands, the entroid of the orrespondingly deteted soures is inonsistent with the PWN (and the putative pulsar) CXOU J061705.3+222127, disovered
by [Olbert
et al.
2001℄, and lying nearby. Both the 3EG and the GeV soure in the
atalogs of [Hartman
et al.
1999℄ and [Lamb & Maomb 1997℄, whih are o-spatial,
are inonsistent with the PWN loation. Similarly, the position of the PWN is separated from
Fermi
Fermi
o
LAT soure by 0.26 , or
∼11σ
away from the loalization of the
LAT peak.
Also at higher energies, the gamma-ray emission observed by VERITAS and
MAGIC is oset from the loation of the PWN by
10 − 20
armin. This latter fat
ould be understood in ase the PWN is a gamma-ray emitter, like in HESS J1825137 [Aharonian
et al.
2006b℄ or HESS J1908+063 [Aharonian
ilar osets were found, see also [Abdo
et al.
et al.
2009℄ where sim-
2010h℄. The emission ould be onsistent
with a senario in whih the VHE emission arises from inverse Compton sattering
o eletrons aelerated early in the PWN's life.
However, if one would assume that the PWN CXOU J061705.3+222127 is produing the emission (note that pulsed radiation from this objet has not been found
at any frequeny), the highest energy TeV-band radiation should peak there: it ould
be extended, but due to losses, as the energy inreases, the emission should be maximum towards the PWN. Moreover, the GeV radiation should be an unresolved pulsar
emission: it should also peak there and be pulsed, see [Bartko & Bednarek 2008℄.
Therefore,
Fermi /VERITAS
data guarantee that the GeV and TeV emissions de-
teted do not originate in the PWN.
4.2 Comparison with nominal model
First of all, the preditions made in Chapter 3 are ompared to/with the most
reent results obtained by VERITAS and
Fermi.
In the ase of VERITAS, given
that their measured SED is ompatible with the earlier one obtained by MAGIC,
no signiant dierene in the response of the models is expeted. In the ase of
44
Chapter 4. The GeV to TeV onnetion in SNR IC 443
Figure 4.1: Earlier MAGIC and EGRET (stars and diamonds, respetively), and
reent
Fermi
LAT and VERITAS (squares and upper trianges, respetively) mea-
surements of the neighborhood of IC 443 as ompared with model preditions for an
impulsive and a ontinuous aelerator, as onsidered in Chapter 3. The nominal
values of parameters for these models are the same as in Figure 3.3, although here
the dierent ontributions are summed up. See the text for details.
Fermi, the situation is dierent beause Fermi
LAT results have extended the energy
domain of the SED muh beyond what was possible for EGRET. Thus, the explored
models in Chapter 3 were unonstrained for that energy range.
In the model presented in Chapter 3, IC 443 was onsidered both as a ontinuous and an impulsive aelerator, as explained in Setion 3.3.1. CRs were assumed to propagate with a diusion oeient at 10 GeV, e.g.,
and
δ = 0.5
in a medium of typial density.
for nulear loss
tor.
τpp
D10 = 1026 m2 s−1 ,
In this medium, the timesale
is orders of magnitude larger than the age of the aelera-
The nominal models also explored the possibility of having dierent dis-
tanes between the SNR shok and the interating louds,
sumptions on the moleular
mass aeted
by the CRs.
together with asThese assumptions
were based on the observations of moleular lines towards the region IC 443
made by, e.g., [Cornett
Seta
et al.
emerges:
et al.
1977, De Noyer & Frerking 1981, Dikman
et al.
1992,
et al. 2003℄. From these studies, the overall piture
∼ 1.1 × 104 M⊙ plaed mostly at the foreground of
1998℄ and [Torres
a total mass of
the remnant, sine the optial and X-ray radiation appear absorbed, with smaller
loud(s) loated loser to the SNR. However, there are several unertainties at play:
whether there is one or several foreground louds, the distane between the foreground loud(s) and the SNR shell, the number and spei loation(s) of the foreground loud(s), and their mass distribution if more than one loud is present.
Fermi
LAT data is expeted to eluidate some of these parameters by a posteriori
omparison with data, regarding not only the moleular environment but also the
diusion properties of the medium.
Figure 4.1 shows the result of the nominal model preditions (theoretial
urves are exatly as in Figure 3.3, from Chapter 3, exept for the fat that all
ontributions are summed up), ompared with the newest data.
The eletron
bremsstrahlung ontribution, visible only at the smallest energies, an hardly explain
4.3. Using Fermi LAT data to onstrain model parameters
45
the whole of the observed IC 443 gamma-ray emission, a onlusion also reahed by
[Abdo
et al.
2010g℄, and previously by [Butt
et al.
2003℄ but with EGRET data. In
the present model, the bremsstrahlung ontribution is onsidered for primary partiles with a proton to eletron ratio of 150, following [Torres 2004℄ formulae. The
ross setion of bremsstrahlung and pion prodution are similar at the
Fermi
LAT
range. Hene, the bremsstrahlung to pion ratio an be approximated with the ratio
of CR eletron and proton uxes (whih is almost 0.01). The observed gamma-ray
ux is too high for bremsstrahlung to be the dominant proess, although it has likely
a non-negligible ontribution below 200 MeV.
The urves in Figure 4.1 are based on assuming 8000 M⊙ at the dierent distanes
enumerated in the plot and a few hundred M⊙ loated loser to the SNR (as for
example,
∼700 M⊙ for the
3 − 4 p).
ase, loated at
ase of an impulsive, and
∼300 M⊙
for a ontinuous
What is striking to the eye is that the previous good
agreement between theory and the observations performed by EGRET and MAGIC
(and obviously VERITAS), partiularly in the ase of the impulsive aelerator,
is now in disagreement with
Fermi
LAT data. The spetrum is harder than that
suggested by EGRET, presenting an almost at SED up to 10 GeV, with a roll-over
in the spetrum between 10 and 100 GeV. The models in Chapter 3 are unable to
reprodue the details of these trends. In fat, the ase of ontinuous aeleration
was already disfavored in Chapter 3 due to both, the middle age of the remnant and
the behavior at the highest energies, whih were produing a muh harder SED than
that observed. This ase is now denitely ruled out, and will not be onsidered any
further. In the ase of impulsive aeleration, it is at the earlier unexplored region
of energies, between 10 and 100 GeV, where signiant deviations between theory
and data are found. There is no model among the ones explored above whih an
aommodate at the same time a SED that is both, suiently steep at VHEs to
onur with MAGIC/VERITAS observations and suiently at at lower energies
to onur with
Fermi
LAT data.
4.3 Using Fermi LAT data to onstrain model parameters
Although the previous setion seems to present a diult-to-solve failure of the
senario, the atual failure omes only from some numerial values of parameters.
In partiular, dierenes in the loation and masses of the overtaken louds an
move the peaks of their orresponding ontributions, see [Aharonian & Atoyan 1996,
Gabii & Aharonian 2007, Rodríguez Marrero
tailed analysis of the dependenes.
et al.
2009℄ and this Chapter for de-
Certainly, kinemati distane estimations are
not aurate enough to obtain the exat separation of the loud(s) from the SNR
shell.
Thus,
Fermi
observations hold the key to make some preisions on the as-
sumptions made in this sense, given that the unknowns an aet the nal results on
the predited spetra. Using
giant loud (e.g.,
∼5300
Fermi
LAT results, we nd that a loser less massive
M⊙ at 10 p) is being overtaken by CRs diusing away
46
Chapter 4. The GeV to TeV onnetion in SNR IC 443
Figure 4.2:
As in Figure 4.1, summed results (right) are produed by two main
omponents (left) oming from a giant loud in front of the SNR, whih is at least
partially overtaken by the diusing osmi rays (∼5300 M⊙ at 10 p) and a loserto-the-shell loud (at 4 p, with 350 M⊙ ), similar to the previous examples.
The
dotted and dashed lines at the VHE range orresponds to dierent normalizations,
∼4000 and ∼3200 M⊙
D10 = 1026 m2 s−1 .
whih an also be understood as interating masses of
same distane. The diusion oeient is as before,
at the
from IC 443. In addition, a smaller amount of moleular material in loud(s) loser
to the SNR shell (e.g., at 4 p, with 350 M⊙ ).
The ombination of both produe
an exellent math to the whole range of observations, see Figure 4.2.
amount of mass than the total quoted:
1.1 × 104 M⊙
A smaller
in the foreground giant
moleular loud(s) being overtaken by diusing CRs from IC 443 is perfetly possible, despite the various unertainties in the absolute position of the loud, its real
number, and the veloity model used; and essentially, due to the fat that the total
amount of mass orresponds to a larger projeted sky area. Whereas this implies no
substantial hange to the model, it allows a math with data at all high-energy frequenies, as shown in Figure 4.2. In this Figure, the non-solid lines at the VHE range
orresponds to dierent normalizations, whih an also be interpreted as dierent
interating masses, of
∼4000
and
∼3200 M⊙
(dotted and dashed, respetively), at
the same distane. The diusion oeient is as before,
D10 = 1026 m2 s−1 .
4.4 Cosmi-ray distributions and their eets
In Figure 4.3, the distribution of CRs appears as generated by the impulsive aelerator (IC 443) at the two dierent distanes onsidered for the moleular mass
distribution in the model of Figure 4.2 (solid blak line). Moreover, the ratio of these
distributions with respet to Earth's osmi-ray distribution is also shown. The key
issue extrated from these plots is that the osmi-ray energy density is greatly
enhaned along the energy range of interest as ompared to that in our viinity, desribed with a spetrum of the form
(e.g.
[Dermer 1986℄.
−2.75
−2 GeV−1 s−1 sr−1
J⊙ (E) ∼ 2.2EGeV
m
Another relevant aspet is that signiant deviations of the
osmi-ray density are obtained when the diusion is slower (i.e.,
a xed SNR age of 30 kyrs, inreasing
D10
D10
is larger). At
produes a displaement of the gamma-
4.4. Cosmi-ray distributions and their eets
47
Figure 4.3: Cosmi-ray spetrum generated by the impulsive aelerator (IC 443)
at the two dierent loud distanes onsidered in Figure 4.2: 10 (solid) and 4 p
(dashed), at the age of the SNR, as a funtion of energy.
results for dierent diusion oeients (blak,
1027 m2 s−1 ).
D10 =
Dierent olors show
1026 m2 s−1 ; and red,
D10 =
The right panel shows the ratio between the osmi-ray spetra of
the left panel, and the osmi-ray spetrum near Earth, as a funtion of energy.
Figure 4.4:
Example of a model output with
D10 = 1027 m2 s−1 .
The dierent
urves represent results for the loation of the giant moleular loud at 10, 15,
20, 25, 30 p from the SNR shell, whereas the lose-to-the-SNR loud is at 4 p.
Neither in this nor in any other of the studied models, the VHE soure spetrum
an be reprodued by varying the parameters with suh a diusion oeient sale.
Furthermore, the resulting SED in the
math the data.
Fermi
LAT range is not hard enough to
48
Chapter 4. The GeV to TeV onnetion in SNR IC 443
Figure 4.5: Contour plot depiting the position of the peak of the SED generated
by a 30 kyrs old injetion interating with louds at dierent distanes, for a range
of diusion oeient sale,
D10 .
ray emission predition to smaller energies, typially, up to
D10 > Dtransition , where
peaks generated by louds at large separation (e.g, 100 p) shift up and peaks generated by louds at smaller separation (e.g., 10 p) shift down in the SED (e.g.,
[Rodríguez Marrero
et al.
2009℄ and referenes therein). This fat implies that, for
the range of distanes onsidered for the giant and lose-to-the-SNR moleular louds
(10 30 p and 2 6 p, respetively), there is no solution with large
D10
able to
t the whole range of data. This was already suggested in Chapter 3, where it was
possible to set a strong onstraint over the diusion timesale, using MAGIC data
only.
D10
26 m2 s−1 . If the separation between the giant
should be of the order of 10
loud and the SNR is greater than 10 p, a slower diusion would not allow suient
high energy partiles to reah the target material and it would be impossible to reprodue the VHE data. On the other hand, the separation between the foreground
loud(s) and the SNR shell an not be muh smaller than 10 p, given that there is
a displaement between the entroid positions of EGRET/Fermi and VHE soures
and that moleular material is absorbing lower frequeny emission from the remnant. The urrent
Fermi
LAT data emphasizes this onlusion. Figure 4.4 shows
an example of a full range of models onstruted with
disagreement with data.
D10 = 1027 m2 s−1 ,
and its
Note that even if the urves are resaled and assuming,
for instane, a muh higher moleular mass (whih would itself be in onit with
multi-frequeny observations), it is not possible to obtain a good t aross the whole
range of observations.
Figure 4.5 presents a ontour plot of the energy at whih the maximum of the
SED is found for the ases of impulsive aeleration of CRs. The age orresponds to a
SNR like IC 443, and the CRs are interating with louds at dierent distanes, for a
range of diusion oeient sale,
D10 , from 1025
to 10
27 m2 s−1 . This plot is useful
4.5. Degeneraies and unertainties
49
Figure 4.6: Examples of solutions around the disussed main values, exploring the
degeneraies (or unertainties) in determining the numerial values of model parameters mathing the observational data. The order of the panels in this plot, top to
bottom and left to right, orresponds with the parameters desribed in Table 4.5, being eah olumn one of the three groups therein. Adapted from [Torres
et al.
2010℄.
to understand whih is the favored solution and its degree of unertainty/degeneray.
In order to t the ombined MAGIC/VERITAS and
is needed to produe a peak at about the
Fermi
Fermi
LAT data, a giant loud
spetral turnover. This implies that,
by looking at the plot, there is either a very large separation between the loud and
the SNR shell for a high
lower
D10 .
D10 ,
or a smaller distane with a faster diusion, i.e. a
The rst option is disarded beause it is not possible to t the VHE
data in this onguration, whereas the latter is the favored solution in this study.
4.5 Degeneraies and unertainties
Figure 4.6 explores the range of parameters around the solutions mathing the observational data.
The aim is to show the degeneraies (or unertainties) within
50
Chapter 4. The GeV to TeV onnetion in SNR IC 443
whih this model provides a reasonable agreement with observations.
Given the
distanes to eah of the louds, the values of masses and diusion oeients used
in Figure 4.6 to obtain good data-mathing are displayed in Table 4.5. Fits ould be
onsidered good for distanes to the giant moleular loud,
DGM C ,
between 9 and
11 p. For an average distane of 10 p, the mass in the lose-to-the-SNR loud (or
louds) dereases the farther the loud is, as shown in the seond olumn of Figure
4.6. For these ases, good solutions with
DGM C
between 9 and 11 p (i.e., 10 p) an
always be found, adjusting other parameters, an example of whih appears in the
seond olumn of Figure 4.6. The average model explored in Figure 4.2 orresponds
to the model 3 in Table 4.5 with:
onstruted with
∼5300, ∼4000,
DGM C = 10 p, dsnr = 4 p, and
∼3200 M⊙ , and Msnr = 350 M⊙ .
the three urves
The results in the third olumn of Figure 4.6 and bottom group in Table 4.5 show
that the smaller the diusion oeient, the worse is the t at VHEs, overprediting
the data. Correting this via a mass adjustment would in turn make for a poor t
at lower energies. Thanks to this, a lower limit to the diusion oeient
be imposed. On the other hand, when
D10
D10
an
inreases, the VHE spetra is quikly
underpredited, and again, orreting this via a mass adjustment would not provide
a good t at lower energies.
In summary, in order for this model to math the multi-frequeny observational
data, the range of variation in the parameters beomes onstrained as
11 p;
3
. dsnr . 6 p,
and
1026 m2 s−1 .
D10 ∼
D10 and
onstitute a diret estimation of
9 . DGM C .
Therefore, these parameters
the moleular environment in the IC 443
viinity, under the assumed validity of this model.
As mentioned before, the gamma-ray emissivity was assumed to be onstant
within the louds; i.e., there is no signiant osmi-ray gradient in the target. This
assumption is an approximation, and it improves whenever the size of the loud is
less than the distane to the aelerator and the diusion oeients inside and
outside the loud are not signiantly dierent (or even if they are, the protonproton timesale is larger than the time it takes for osmi rays to overtake the
whole loud). In the ase of IC 443, these onditions an be aommodated for the
solutions in Table 4.5, exept perhaps for the very massive loud loated lose to
the SNR at dsnr =2 p. For this massive lose-to-the-SNR loud, it would imply an
average density higher than that usually found, although even this might also be
possible given the small sale lumps found therein, see e.g., [Rosado
et al.
2007℄.
4.5.1 Inuene of the δ -parameter
In addition, other parameters of the model are explored, partiularly those inuening the way in whih the diusion oeient varies with energy (the parameter
δ),
or the injetion spetrum of osmi rays (referred to as
values appear to be rather onstrained. For instane, the
be around
δ = 0.4 − 0.7,
e.g., [Berezinskii
et al.
δ
α).
Their orresponding
parameter is expeted to
1990℄, and a typial value of 0.5 is
usually assumed. Figure 4.7 gives aount on how small variations in
δ
hange the
slope of good-tting solutions to the high and very-high energy data. One an see
4.5. Degeneraies and unertainties
51
Table 4.1: Main model parameters for solutions shown in Figure 4.6, exept model
3, whih instead is shown in Figure 4.2.
DGM C
and
dsnr
are the distane to the
GMC and the loser-to-the-SNR moleular louds. The three quoted
MGM C = (1/f )
f
values dene
8000 M⊙ . The three groups explore dierent degeneraies: in the
position of the GMC, in the position of the smaller loud, and on the diusion
oeient.
Model
1
2
3
4
5
6
7
8
9
10
11
12
13
that for steeper
DGMC
p
8
9
10
11
12
10
10
10
10
10
10
10
10
δ-parameters,
dsnr
p
4
4
4
4
4
2
3
5
6
4
4
4
4
D10
m2 s−1
1026
1026
1026
1026
1026
1026
1026
1026
1026
8 ×1025
9 ×1025
2 ×1026
3 ×1026
5.0
3.2
2.5
1.8
1.3
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
Msnr
M⊙
350
350
350
350
350
1750
580
250
195
350
350
350
350
steeper gamma-ray spetra are found. If the masses
of the moleular louds are maintained and
one would need an even lower
3.0
1.8
1.5
1.0
0.7
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
f
...
4.0
2.5
2.0
1.4
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
D10
δ
(lower than
is larger, in order to have a good t
D10 = 1026 m2 s−1 ,
see Figure 4.6),
obtaining a less plausible solution.
4.5.2 Unertainties due to the ross setion parameterization
Another hek is performed to nd out whether hanges in the ross setion parameterization an produe signiant variane in the results.
In the appendix
of [Domingo-Santamaría & Torres 2005℄, the dierent predited yields in gammarays obtained when using alternate ross setion parameterizations (known bak
then) were ompared among themselves and with the data.
rameterizations therein were:
the one introdued by [Kamae
The onsidered pa-
et al.
2005℄, the
δ-
funtional form by [Aharonian & Atoyan 1996℄ that is used above, the one by
[Stephens & Badhwar 1981℄, and [Blattnig
was found that Kamae's and the
et al.
δ-funtional
2000a, Blattnig
et al.
2000b℄.
It
form mathed quite well. Figure 11 of
that study showed this by plotting the gamma-ray emissivities obtained with the orresponding use of eah of the parameterizations of the ross setion. In addition, it
was also found that neither the parameterizations from [Stephens & Badhwar 1981℄
nor from [Blattnig
et al.
2000a, Blattnig
et al.
2000b℄ were appropriate for their use
in broad-band high-energy modeling suh as the one pursued here. More reently,
52
Chapter 4. The GeV to TeV onnetion in SNR IC 443
Figure 4.7: Comparing gamma-ray yields with dierent
right
δ = 0.4,
[Kelner
et al.
δ
parameters, from left to
0.5, 0.6, and 0.7. The other parameters are as in Figure 4.2.
2006℄ presented a new approah for obtaining the ross setion in
pp
interations. These authors used two shapes for representing the ross setion, separated in energy. At low energies (up to 100 GeV), Kelner et al. approah uses a
slightly modied but similarly-shaped
δ-funtional form.
At higher energies, the ap-
proah is dierent, and presents an analytial shape that ts the results of the simulations of the energy distribution of
π mesons by the SYBILL ode.
Figure 4.8 shows
a omparison of the ross setion parameterizations used in the previous gures, the
δ-funtional
form by [Aharonian & Atoyan 1996℄, with that of [Kelner
Dierenes are within 20%, with the
δ-funtional
et al.
2006℄.
approximation being larger.
Hene, the onomitant hange in ux preditions, due only to dierent ross
setion parameterizations, an be reabsorbed as part of the unertainty in the determination of the model. Figure 4.9 shows the impat of this in two ways.
The
left panel shows several alternatives for the position of the large (TeV-produing)
loud in the model, loated at 10, 15, and 20 p.
Here, the mass of this loud is
maintained xed, and only the shape of the urves for dierent distanes is important. It is lear that the hange in ross setion parameterization does not enable
any of the previous models to be feasible. Also, it singles out a distane of about
10 p from the SNR shell to the giant TeV-produing loud for obtaining a good t.
The right panel assumes this distane of 10 p and explores the unertainty in the
determination of the giant loud mass. The parameters therein shown are 4 p and
350 M⊙ for the lose-to-the-remnant loud (the same as in the left panel), and 10 p
and 7272, 5333, 4210 M⊙ for the TeV-produing giant loud.
4.5. Degeneraies and unertainties
53
Figure 4.8: Comparison (left) and ratio (right) of the ross setion parameterizations
used in the previous Figures, the
with that of [Kelner
et al.
δ-funtional
form by [Aharonian & Atoyan 1996℄,
2006℄.
Figure 4.9: Left: Gamma-ray ux results using the [Kelner
et al.
2006℄ approxima-
tion for dierent distanes from the shell to the TeV-produing loud, 10 (solid),
15 (dotted) and 20 (dashed) p.
The lose-to-the-remnant loud is xed at 4 p
and ontains 350 M⊙ hanges in this latter value do not improve the overall t.
Right: Gamma-ray ux results using the parameterization from [Kelner
et al.
2006℄
for dierent values of the giant loud mass plaed at a xed distane of 10 p (see
text for details).
54
Chapter 4. The GeV to TeV onnetion in SNR IC 443
Figure 4.10: Eletrons (eletrons and positrons are shown together), photons and
two avors of neutrinos produed within the louds onsidered nearby IC 443, using
a set of parameters shown in Figure 4.9 (right panel) with mass of the giant loud
equal to 7272 M⊙ . The
νµ
and
νe
neutrino urves show both the partile and the
anti-partile ux. Data should only be ompared with the photon urve.
4.6 Computation of seondaries other than photons
Using the parameterization from [Kelner
than
photons
[Gabii
et al.
an
be
readily
et al.
omputed,
and
2006℄, seondary partiles other
this
is
shown
in
Figure
4.10.
2009℄ showed, by testing a wide range of parameters, that seondary
eletrons produed within louds an esape without being aeted by signiant
losses. In other words, that the propagation time through the loud for osmi-ray
eletrons is shorter than the energy loss time for partile energies between
∼ 100 MeV
and few hundreds of TeV. Thus, there would be little eet of the seondary eletrons produed on the non-thermal emission from the loud. In addition, for typial
3
densities of louds, in the several hundred to several thousand partiles per m , the
dominant energy loss from
∼
100 MeV and
∼
10 TeV would be bremsstrahlung and
not synhrotron.
Nonetheless, a onlusive proof of the hadroni nature of the gamma-ray emission ould ome from the detetion of neutrinos,
ν.
Neutrino telesopes searh for
up-going muons produed deep inside the Earth, and are mainly sensitive to the
inoming ux of muoni neutrinos,
νµ ,
and their antipartiles,
ν̄µ .
The nished
IeCube experiment, for example, will onsist on 4800 photomultipliers, arranged
on 80 strings plaed at depths between 1400 and 2400 m underneath the South Pole
ie, e.g., [Halzen 2006℄. The strings will be loated in a regular spae grid overing
2
a surfae area of 1 km .
Eah string will have 60 optial modules (OM) spaed
17 m apart. The number of OMs whih have seen at least one photon is alled the
hannel multipliity,
Nch .
Note that eah photon omes from Cherenkov radiation
4.7. Conluding remarks
55
that has been produed by the muon whih, in turn, results from the interation
of the inoming
to
Nch = 10,
ν
inside the earth and ie rust. The multipliity threshold is set
whih orresponds to an energy threshold of 200 GeV. The angular
resolution of IeCube will be around
∼ 0.7◦ .
A rst estimation of the event rate of the atmospheri
ν -bakground that will
et al. 2003℄, as:
be deteted in the searh bin an be obtained, e.g., [Anhordoqui
Z
dΦB
dN Pν→µ (Eν ) ∆Ω ,
dEν
= Aeff
dt B
dEν
(4.1)
∆Ω ≈ 1.5 × 10−4 sr is the angular
−3.21 GeV−1 m−2 s−1 sr−1 is the
size of the searh bin, and dΦB /dEν . 0.2 (Eν /GeV)
νµ + ν̄µ atmospheri ν -ux [Volkova 1980, Lipari 1993℄. Here, Pν→µ (Eν ) denotes the
probability that a ν of energy Eν on a trajetory through the detetor, produes a
3
−13 (E /GeV)2.2 , whereas
muon. For Eν ∼ 1−10 GeV , this probability is ≈ 3.3×10
ν
0.8
−6 (E /TeV)
for Eν > 1 TeV , Pν→µ (Eν ) ≈ 1.3 × 10
[Gaisser et al. 1995℄. On the
ν
other hand, the ν -signal is similarly obtained as
Z
dN dEν (Fνµ + Fν̄µ ) Pν→µ (Eν ) ,
(4.2)
= Aeff
dt S
where
Aeff
is the eetive area of the detetor,
(Fνµ + Fν̄µ ) is the inoming νµ -ux. In the previous integrals, both expresPν→µ (Eν ) are used aording to the energy, and integrated from 200 GeV
up to 10 TeV. The eet of ν -osillations is taken into aount following table 2 of
[Cavasinni et al. 2006℄, where the osillation probability in the average vauum oswhere
sions for
illation hypothesis is given. The inter-onversion probability between avours and
between anti-avours is assumed to be the same.
As an eet of osillations, the avour omposition of all the expeted uxes
for eah avour are within 50% of eah other.
Using the former equations and
the seondary omputation shown in Figure 4.10, the number of muon neutrino
signal events is found to be 0.6 per year of observation.
This is still signiantly
below the estimation of the number of bakground events, whih under the previous
provisions is 6.4 along the same period with the full IeCube array. If only events
above 1 TeV are onsidered, the expeted signal is 0.25 yr
−1 , and the omputed
−1 . IeCube does not seem to be able to distinguish this signal
bakground is 1.92 yr
in reasonable integration times, at least within the reah of this simplied treatment
of the detetor.
4.7 Conluding remarks
The reent observations of the IC 443 environment made by AGILE,
Fermi
LAT,
and VERITAS at the GeV and TeV energies, are spetrally onsistent with the
interpretation of osmi-ray interations with a giant moleular loud lying in front
of the remnant. This senario would be produing no signiant ounterpart at lower
energies at that loation, and thus would be leading to a natural interpretation of
56
Chapter 4. The GeV to TeV onnetion in SNR IC 443
the displaement between the entroids of the detetions at the dierent energy
bands. Using the latest data, the diusion harateristis in this environment were
estimated, within the assumed validity and framework of this model. The results
show that the diusion oeient is lower and the osmi-ray density is higher
than the Earth-values of both magnitudes.
Unertainties in the amount and the
loalization of the target moleular mass still remains.
Just as well, the density
at whih this moleular material is found remains unknown.
For instane, the
unertainty in the osmi-ray-overtaken mass disussed in the previous setions is
about 100% for mathing models at the extremes of this parameter.
But even
allowing for suh a wide range, the model ould aommodate some but not all
variations in other parameters, with the values of
shell seemingly being solid onstraints.
D10
and distanes from the SNR
Chapter 5
Starburst galaxies
Contents
5.1 Introdution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.2 Theoretial model . . . . . . . . . . . . . . . . . . . . . . . . . 58
5.3 M 82 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.3.1
Comparison with previous studies . . . . . . . . . . . . . . .
63
5.3.2
Results and Disussion . . . . . . . . . . . . . . . . . . . . . .
64
5.4 Disovery of HE and VHE emission from starbursts . . . . 74
5.4.1
Gamma-ray emission deteted from M82 . . . . . . . . . . . .
74
5.4.2
NGC 253, onfronted with the model . . . . . . . . . . . . . .
74
5.5 Conluding remarks . . . . . . . . . . . . . . . . . . . . . . . . 77
5.1 Introdution
Starburst
soures
galaxies
[Paglione
et al.
have
1996,
been
Blom
Domingo-Santamaría & Torres 2005,
strumental sensitivity.
et al.
antiipated
1999,
Persi
et al.
as
Torres 2004,
2008℄,
gamma-ray
Torres
provided
et al.
2004,
suient
in-
Suh galaxies have an enhanement both in the star
formation and supernova (SN) explosion rate, and dense (gas and dust enrihed)
environments.
These harateristis suggest that they should emit gamma rays,
and their luminosity would be greater than normal galaxies. SN remnants (SNR)
and shok winds from massive stars are supposed to aelerate osmi rays (CR).
Very energeti gamma rays are produed due to CRs ollisions with ambient nulei
and subsequent
π0
deay. Those gamma rays an be deteted both with spae-born
and ground-based imaging atmospheri Cherenkov telesopes.
With the arrival of the
Fermi
satellite, and the seond-generation of Cherenkov
telesopes (H.E.S.S., VERITAS, MAGIC) at their full potential, it is important
to have the most detailed model for these astronomial objets to obtain a proper
feedbak from observations and improve our knowledge of the osmi-ray population
and the physial environment of nearby starbursts. Furthermore, with the reent
on-going disussions [Loeb & Waxman 2006, Steker 2007, Anhordoqui
et al.
2008℄
about the starbursts ontribution to the neutrino bakground, it is important to
have onsistent and detailed models of neutrino prodution in spei galaxies. The
58
Chapter 5. Starburst galaxies
assumptions made in previous studies are disseted, while observational detetability
3
with, e.g., km -observatories is onsidered.
Reently, the detetion of M82 was reported by the VERITAS ollaboration,
while gamma rays above hundreds of GeVs oming from the fainter NGC 253 were
laimed by the H.E.S.S. ollaboration.
During the same epoh, the
Fermi
exper-
iment presented the data olleted at lower energies oming from the diretion of
both starburst galaxies [Abdo
et al.
2010℄. Minor and reasonable variations in the
parameter spae of already published models [Domingo-Santamaría & Torres 2005,
de Cea del Pozo
et al.
2009b℄ an fully aount for the high and very high energy
emission oming from both galaxies, while agreeing with previous data deteted from
radio to infrared (IR). This Chapter presents the model that, prior to the detetions, predited the gamma-ray emission from M82 [de Cea del Pozo
et al.
2009b℄,
and the possible parameter variations to better aknowledge those detetions
[de Cea del Pozo
et al.
2009a℄.
5.2 Theoretial model
The aim of this study is to obtain multi-frequeny/multi-messenger preditions for
the photon and neutrino emission oming from the entral region of M82, where the
inner starburst is loated. The model seeked is intended to be onsistent, with all
the dierent omponents of the emission from radio to TeV photons and neutrinos
traked to one and the same original osmi-ray population. This population is
a onsequene of all eletromagneti and hadroni hannels from the primary and
subsequently-produed seondary partiles.
With this model at hand, a range of
unertainties in the parameters an be explored, orrespondingly shifting upwards
or downwards the high energy end of the spetrum.
In order to perform suh study, the ode
adapted in several ways.
Q-diffuse
Q-diffuse
[Torres 2004℄ has been
solves the diusion-loss equation for eletrons
and protons and nds the steady state distribution for these partiles subjet to
a omplete set of losses in the interstellar medium (ISM). Subsequently, it omputes seondary partiles from hadroni interations (neutral and harged pions)
and Coulomb proesses (eletrons), and gives aount of the radiation or deay
produts that these partiles produe. Seondaries (photons, muons, neutrinos, eletrons, and positrons) that are in turn produed by pion deay are also alulated.
Additional piees of the ode provide the dust emissivity, and the IR-FIR photon
density, whih is onsistently used both as target for inverse Compton sattering
and for modeling the radiation at lower frequenies. For radio photons, synhrotron
radiation, free-free emission, and absorption are omputed using the steady distribution of eletrons. Finally, and using the radiation transport equation, opaities
to
γγ
and
γZ
proesses, as well as absorbed gamma-ray uxes, are alulated. The
implementation of
Q-diffuse
inludes several upgrades.
Some are stritly teh-
nial, allowing for a more versatile and automati input-output interation. Some
are physial: neutrino-prodution subroutines have been developed for all neutrino
5.2. Theoretial model
59
hannels in the deay of positively and negatively harged pions and a reent parameterization of
Q-diffuse
pp
interations by [Kelner
et al.
2006℄ has been used. The ow of the
ode is shown in Figure 5.1. Several loops an be distinguished there:
they are used in order to determine a self-onsistent set of parameters, suh that all
preditions for the dierent bands of the eletromagneti spetrum are onsistent
with the data.
Previous studies of diuse high energy emission, and of eletron and positron
prodution, with dierent levels of detail and aims, go bak to the early years
of
gamma-ray
astronomy.
A
summary
of
these
rst
eorts
is
summarized
by [Fazio 1967, Ginzburg & Syrovatskii 1964℄ and [Ramaty & Lingenfelter 1966℄,
then followed by [Marashi
et al.
1968, Steker 1977℄, among many others.
Se-
ondary partile omputations have a similarly long history see, e.g., [Steker 1970,
Orth & Bungton 1976℄. Relatively more reent eorts inlude [Drury
Moskalenko & Strong 1998,
[Fatuzzo & Melia 2003℄.
used by [Paglione
bursts galaxies.
et al.
Strong & Moskalenko 1998,
Marko
et al.
et al.
1999℄
1994,
and
The general ideas followed in those works were already
1996℄ and [Blom
et al.
1999℄ when modeling nearby star-
On the other hand, the present study losely traks ideas from
[Brown & Marsher 1977℄ and [Marsher & Brown 1978℄, regarding their studies of
lose moleular louds.
An important aspet of this approah is that it laks detail in modeling single
soures.
Isolated SN explosions, or SNRs, or even the impliation of those SN
exploding within the wind bubbles of their progenitors and the onurrent losses in
these environments are not treated by themselves. On the ontrary, the emphasis
lies on average properties of the whole starburst region, seen as a CR injetor.
Mixing these two aims would require an eort that is beyond urrent observational
apabilities of what is known in starburst galaxies, as well as beyond what is possible
for this work. Essentially, to make quantitative estimates in suh small-sale detail,
one would need to understand the features of eah and all the SN explosions in
these kind of galaxies, and model them individually and aurately.
From that
point (i.e., from a staking of a soure-by-soure modeling), an averaged senario
ould be built.
This has not been ahieved even for our own Galaxy.
Similarly,
the present approah to the modeling of the super-wind is also simple, in order to
enompass it with the rest of the omponents of the model. See [Everett
et al.
2008℄
for a more detailed analysis of the properties of the Galati super wind, and also
[Gallagher & Smith 2005℄.
The assumption of a uniform distribution of aelerators in the inner region of
the starburst justies having a steady state distribution therein.
Also, this dis-
tribution an be omputed via solving the full diusion-loss equation.
Partiles
with energies of 100 TeV have a range omparable to or greater than the size of the
Galaxy, whereas the distanes travelled by hadroni partiles injeted with energies
of the order of tens of GeV do not exeed
1 − 2 kp.
For eletrons, the situation is
even more ompliated (see later in this setion), due to the more signiant losses
they suer. TeV-energy eletrons ool down so quikly due to synhrotron and inverse Compton losses that they annot diuse beyond few hundred parses from
60
Chapter 5. Starburst galaxies
CR injection spectrum (SN rate,
primary protons:
Q
inj
...)
primary electrons:
(E )
p
eff
p
Q
inj
(E ) N /N
p
p
p
e
DIFFUSION-LOSS Equation
- Losses and confinement timescales from
production, diffusion, convection
e
charged pion decay:
p
initial injection proton slope, N /N
ionization,
Emission:
0
+
decay
,
,
,
decay:
p
p
production
+
+
knock-on:
-
e production
Data fitting
hadronic interactions with ISM:
production
N (E )
steady proton spectrum:
spectrum
-
e , e production
secondary electrons/positrons:
sec
Q
e
(E )
e
DIFFUSION-LOSS Equation
Dust
Emission
-ray spectrum
IR spectrum
Bremsstrahlung, IC
Emission: Synchrotron +
N (E )
e
e
Absorption:
Free-free
-ray spectrum
radio spectrum
IC target photon field
EM
steady electron/positron spectrum:
Emission:
Data fitting
inverse Compton, adiabatic, diffusion, convection
e.g., magnetic field B
- Losses and confinement timescales from ionization, synchrotron, bremsstrahlung
photon field for IC losses
Absorption processes
-ray spectrum
-ray spectrum
Figure
5.1:
Code
ow
Q-diffuse,
of
[Torres & Domingo-Santamaría 2005℄ to take into aount
adapted
from
new updates devel-
oped for this work.
their injetion site, for typial values of the diusion oeient and of the interstellar magneti/radiation elds. Nonetheless, the limited size and ompatness of
the starburst region is ompatible with a steady state eletron distribution in that
entral region.
The steady-state partile distribution is omputed as the result of an injetion
distribution being subjet to losses and seondary prodution in the ISM. At suiently high energies, the injetion proton emissivity is assumed to have the following
form as a funtion of proton kineti energies:
Qinj (Ep, kin ) = K
where
p
is a power-law index,
K
Ep, kin
GeV
−p
exp
−Ep, kin
Ep, cut
is a normalization onstant,
Ep, cut
(5.1)
is an energy
uto in the aelerated partiles that are injeted (assumed as 100 TeV, with a
range explored below). Units are
value for the normalization,
K,
[Q] =
−1 m−3 s−1 . To get a numerial initial
GeV
its value is assumed to ome from the total power
transferred by supernovae into CRs kineti energy within a given volume. Thus, the
supernova rate is essential to x the level of the osmi-ray sea:
Z
R
Ep, kin, max
Qinj (Ep, kin )Ep, kin dEp, kin ≡
Ep, kin, min
is the rate of supernova explosions,
V
ηPR
.
V
orresponds to its volume, and
transferred fration of the supernova explosion power (P
∼ 1051
(5.2)
η
is the
erg) into CRs. The
5.2. Theoretial model
61
average rate of power transfer is assumed to be 10%. The assumption of the
in 5.1 is not a-priori, but rather an a posteriori hoie.
p value
That hoie is made in
order to get a slightly better t to all the multi-wavelength data, and ats as an
average desription of the injeted osmi-ray sea in the star forming region, where
multiple nearby shoks ould ontribute.
As noted by [Domingo-Santamaría & Torres 2005℄, the distribution of osmi
rays is probably atter at low energies, e.g., it would be given by equation (6) of
[Bell 1978℄, orrespondingly normalized.
Negleting this dierene at low energy
has been numerially veried to not produe any important hange in the omputation of seondaries, and espeially on gamma-rays at the energies of interest. As
in [Berezhko
et al.
2006℄, eletrons are assumed to be injeted into the aeleration
proess at the shok fronts.
The eletron injetion rate is hosen suh that the
eletron-proton ratio is a onstant to be determined from the synhrotron observations. The diusive transport equation takes are of the hanges produed after
injetion onto this distribution.
The diusion-loss equation (see, e.g.,[Ginzburg & Syrovatskii 1964℄ p.
296;
[Longair 1994℄, p. 279) is given by:
− D ▽2 N (E) +
In this equation,
D
N (E)
d
∂N (E)
−
[b(E)N (E)] − Q(E) = −
τ (E)
dE
∂t
Q(E) represents the soure
energy E , τ (E) stands for the
is the salar diusion oeient,
term appropriate to the prodution of partiles with
onnement timesale,
and
of energy.
E + dE
N (E)
is the distribution of partiles with energies in the
b(E) = − (dE/dt) is the rate of loss
b(E), τ (E), and Q(E) depend on the kind of partiles
onsidered. In the steady state, ∂N (E)/∂t = 0, and when the spatial dependene is
2
onsidered to be irrelevant: D ▽ N (E) = 0. Then, the diusion-loss equation an
be numerially solved by using the orresponding Green funtion, G, suh that for
any given soure funtion or emissivity, Q(E), the solution is:
range
E
(5.3)
per unit volume, and
The funtions
N (E) =
Z
Emax
dE ′ Q(E ′ )G(E, E ′ )
(5.4)
E
The onnement timesale will take into aount that partiles an be diusing
away, arried away by the olletive eet of stellar winds and supernovae, or aeted
by pion prodution (for CRs). Pion losses are atastrophi, sine the inelastiity of
the ollision is about 50%. They produe a loss timesale in the form of:
−1
τpp
=
(dE/dt)pion
E
(see, e.g., [Mannheim & Shlikeiser 1994℄.
(5.5)
Thus, in general, for energies higher
than the pion prodution threshold:
−1
−1
τ −1 (E) = τD
+ τc −1 + τpp
.
(5.6)
62
Chapter 5. Starburst galaxies
The onvetive timesale,
[Strikland
et al.
τc ,
is
∼ R/V ,
where
V
is the olletive wind veloity.
−1 for the wind veloity, and this
1997℄ found a value of 600 km s
value is used below. However, the response of the model to an arbitrary doubling
or halving of this value has been studied. The unertainty introdued by varying
the veloity is smaller than that produed by other parameters. Finally, assuming
a homogeneous distribution of aelerators in the entral hundreds of parses of the
starburst galaxy, the harateristi esape time orresponds to the homogeneous
diusion model value ([Berezinskii
τD =
1990℄, p. 50-52 and 78):
R2
τ0
=
2D(E)
β(E/GeV)µ
(5.7)
c, R is the spatial extent of
the region from where partiles diuse away, and D(E) is the energy-dependent
µ
diusion oeient, whose dependene is assumed ∝ E with µ ∼ 0.5, and τ0 is the
harateristi diusive esape time at ∼ 1 GeV. The results ontained in this Chapter
use τ0 = 10 Myr, but a range was explored to judge unertainties. For eletrons, the
where
β
et al.
is the veloity of the partile in units of
total rate of energy loss onsidered is given by the sum of that involving ionization,
inverse Compton sattering, adiabati, bremsstrahlung, and synhrotron radiation.
The Klein-Nishina ross setion is used.
5.3 M 82
M82
is
[Mayya
a
near
et al.
starburst
galaxy.
It
an
be
seen
nearly
edge-on
◦
(77 ,
2005℄) and has a gas ontent mostly onentrated in the inner 2 kp.
This galaxy presents a high luminosity both in the far infrared and X-ray domain:
44 erg s−1 and 1040 erg s−1 respetively, e.g., [Ranalli
10
et al.
2008℄.
As part of the M81 group, M82 shows hints of an enounter with some of its members 1 Gyr ago, speially with the dwarf galaxy NGC 3077 and the former M81,
materialized in an intergalati gas bridge of 20 kp. Up to 10 kp above the plane
of M82, galati superwinds an be deteted. Following HI streamers, the external
part of the disk (>5 kp) presents a warped form.
On the other hand, the inner
part (300 p) harbours a starburst. Around this region, a moleular ring of 400 p
radius and a near-IR bar of
∼
1 kp length an be deteted [Teleso
From the tips of this bar, two symmetrial arms emerge [Mayya
et al.
et al.
1991℄.
2005℄. This
led to a hange in the morphologial lassiation. At rst, an irregular shape was
assumed due to optial appearane: bright star-forming knots interspersed by dusty
laments [O'Connell & Mangano 1978℄. Nowadays, it seems more likely that M82
is a SB galaxy.
[Freedman
et al.
1994℄ established a distane for M81 of 3.63
±
0.34 Mp, thanks to the disovery of new Cepheids by the Hubble Spae Telesope
(HST) in this galaxy.
A few years later, [Sakai & Madore 1999℄ found a distane
of 3.9 (±0.3)random (±0.3)systematic Mp for M82, based on the detetion of the red
giant branh stars using HST photometry.
Both distanes are onsistent within
errors, the latter is the one used in this work.
The starburst region is loated in
5.3. M 82
63
∼300 p, height of ∼200 p, e.g., see
therein, and [Mayya et al. 2006℄. Meanwhile, the
thin disk up to 7 kp, see e.g., [Persi et al. 2008℄,
the inner part of the galaxy, with a radius of
[Völk
et al.
1996℄ and referenes
rest of the emission extends to a
and referenes therein.
A signiant amount of moleular material has been found in the entral region,
where most of the starburst ativity is loated. A disussion on the supernova explosion rate an be found in the setion 5.3.2. The ontent of the gas mass in the whole
2.9× 109 M⊙
et al.
2.9× 108 M⊙ (H2 )
by [Young & Soville 1984℄ to the more reent results found by [Casasola et al. 2004℄
7× 108 M⊙ (HI) and 1.8× 109 M⊙ (H2 ), where dierent assumptions for distane and
the normalization of luminosity were made. [Weiÿ et al. 2001℄ report for the star8
burst region around 2 × 10 M⊙ (H2 ), using separate methods for the determination
of CO and H2 densities. This value essentially agrees with those estimated from 450
µm dust ontinuum measurements [Smith et al. 1991℄ and from CO(2 → 1) intensities [Wild et al. 1992℄, and is, therefore, the one used in the determination of the
−3 ).
uniform density for the model of this Chapter (∼ 180 m
galaxy range from
(HI) by [Cruther
1978℄ and
5.3.1 Comparison with previous studies
A natural omparison an be made between this approah and previous studies of the
entral starburst region of M82, in partiular, [Akyüz
Paglione
et al.
1996℄, and [Persi
et al.
The earlier work made by [Akyüz
et al.
1991, Völk
et al.
1996,
2008℄.
et al.
1991℄ foused on gamma-ray emission
at the GeV regime (integral ux above 100 MeV) and basially provides a simple order of magnitude estimation with data available at that time.
[Völk
et al.
1996℄
also did not provide a multi-frequeny model, but rather onsider only neutral
pion deay from protons to obtain an order of magnitude estimation of the ux
at high and very-high gamma-rays.
This approah was also taken (with mi-
nor dierenes) by [Pavlidou & Fields 2001℄ and [Torres
et al.
2004℄.
These stud-
ies do not inlude a omputation of seondaries and their emission at low energies.
Their aim is dierent than the one in the present work, whih is provid-
ing a onsistent model along the entire eletromagneti spetrum.
[Paglione
et al.
The work by
1996℄ is more omplex, and it was disussed in detail, in parti-
ular, when ompared with results by
Q-diffuse
on Arp 220 and NGC 253, by
[Torres 2004℄ and [Domingo-Santamaría & Torres 2005℄ respetively. There are several dierent physial and methodologial onsiderations embedded in their model
ompared to those assumed here. Moreover, high-energy (TeV) preditions are not
provided. None of these works onsider neutrino emission.
The most reent study on M82, from [Persi
et al.
2008℄, also diers from the
present work in some key parameters and, most importantly, in the method and
assumptions for the modeling.
Among the physial parameters, whih values are
given by Persi et al., the distane (3.6 Mp, whih is atually the one to M81), the
dust emissivity index (σ
= 1),
the proton to eletron primary ratio (Np /Ne
= 200),
the magneti eld (180 µG) and the slope of primary injetion spetrum (2.4) are
64
Chapter 5. Starburst galaxies
all dierent from the ones used or derived in the present Chapter. The dierene
between these (latter) values in [Persi
to x them.
For instane, Persi et al.
et al.
2008℄ omes from the method used
obtained the magneti eld by assuming
equipartition with primary partiles, while the magneti eld in this work is found by
a multi-frequeny analysis that also takes into aount produed seondary partiles.
As Figure 5.2 (left panel) shows, the steady population of eletrons that would result
after solving the diusion loss equation, injeting only primary and only seondary
1
partiles, are omparable. This fat was also found in the ases of other highly-dense
environments, and it implies that it is not a safe assumption to onsider that the
primary population dominates when omputing the equipartition eld.
The path of the numerial treatment by [Persi
presented in this Chapter.
et al.
2008℄ is inverse to the one
In the former study, the normalization of the proton
spetrum is xed starting from an assumed
the normalization for eletrons
Ne
Np /Ne
fator from equipartition, with
in turn obtained from the radio spetrum.
In
the present ase, protons are the starting point, with the supernova explosions injeting primaries whih are left to interat through all possible proesses, produing
eletrons whih in turn generate synhrotron emission. It is this non-negligible ontribution from seondary eletrons what is taken into aount when omputing
and
Np /Ne ,
B
in order for the data to onsistently math at all frequenies (see Fig-
ure 5.1 for further lariation). Neither equipartition is a priori assumed, nor the
primary eletron population is a priori xed from the radio spetrum in the present
approah. Finally, neutrino emission is saled from gamma-ray uxes by Persi et
al., whereas it is omputed using orrespondingly parameterized ross setions up to
tertiary partiles interations in this work. The two approahes the one herein presented and that of [Persi
et al.
2008℄ are in any ase omplementary and provide
onsistent results.
5.3.2 Results and Disussion
The steady population of protons and eletrons of the starburst galaxy M82 omputed in the model is shown in Figure 5.2 (right), where a power-law index
p = 2.1
for the injetion of primary relativisti hadrons is used. An exponential uto is set
to 100 TeV, although no signiant dierene is observed if it is hanged to half this
value, even at energies as high as 10 TeV. Moreover, a range of values is studied for
the normalization fator for the hadroni injetion spetrum, as it depends on other
sensitive parameters subjet to unertainties. For instane, the rate of SN explosion
per year was assumed to be 0.3 in earlier studies, but reently it is more ommonly
referred to as
∼0.1 SN yr−1 .
In the present work, both a high and a low value for the
SN rate are studied, revealing a range of unertainties. This has been represented
in Figure 5.4, where other exponential utos are also onsidered.
Indeed, the disussion about the supernovae explosion rate is on-going.
highest value of 0.3 SN yr
−1 is used by, e.g., [Völk
et al.
The
1996℄ and other authors
1
The seondary partiles in this study are those eletrons and positrons that result from knokon and pion deay proesses in the inner region of M82.
5.3. M 82
65
Figure 5.2: Left: Comparison of the steady population of eletrons that would result
after solving the diuse loss equation injeting only primary (solid blue) and only
seondary (dashed blue) partiles from knok-on and pion deay in the inner
region of M82. The total steady eletron population (solid blak), resulting from the
injetion of both primary and seondary eletrons, is also shown. Parameters used
in this Figure oinide with those presented later within the same model (Figures
5.3 5.4). Right: Steady proton (solid) and eletron (dashed) distributions in the
innermost region of both M82 (blak) and NGC 253 (red).
66
Chapter 5. Starburst galaxies
Figure 5.3: Multi-frequeny spetrum of M82 from radio to infrared. The observational data points orrespond to: [Klein
(irles) and [Förster
et al.
et al.
1988℄ (triangles), [Hughes
The results from modelling orrespond to:
≃ 200 K)
1994℄
synhrotron plus free-free emision
(dashed), dust emission (dotted) splitted in a ool (blue, Tc
(purple,Tw
et al.
2003℄ (squares), and referenes therein in eah ase.
= 45 K)
and a warm
omponent, and the total emission from radio and IR emission
(solid).
thereafter, and it is based on [Kronberg
et al.
1985℄. The latter study has ompiled
−1 by [Kronberg & Wilkinson 1975℄,
−1 , based only on
based on the total non-thermal emission; going up to 0.16 yr
dierent estimations, starting from 0.1 SN yr
IR exess; then 0.2 0.3 by [Kronberg & Sramek 1985℄, based on diret monitoring of variability of disrete soures; and still going higher up to 0.3 SN yr
[Rieke
et al.
−1 in
1980℄, based on estimating the number of new radio soures. But ritis
to [Kronberg & Sramek 1985℄, and in general to high values of the supernova remnant rate, have arised mainly beause the rate of detetion of new radio soures does
et al. 2001, MLeod et al. 1993,
−1 ) have also been
(0.07 − 0.08 SN yr
not orrespond to those values, e.g., see de [de Grijs
Bartel
et al.
1987℄. Lower values for the rates
reently favored by Feneh et al. (2008), who made an 8-days deep MERLIN radio
imaging of SNR in the starburst and use two dierent methods to ompute the
explosion rate. On one side, they assumed that the more radio luminous SNRs in
M82 are younger than Cas A. On the other, they assumed that the SNR are in free
expansion and used the measured
N (< D) − D
plot.
The primary eletron population is taken to be proportional to the injetion
proton spetrum, saled by the ratio between protons and eletrons,
Np /Ne .
The
5.3. M 82
67
Figure 5.4: Left: Energy distribution of the dierential gamma-ray uxes, exploring
a range of unertainties in supernova explosion rate and utos in the primary energy, as it is explained in the text. The sensitivity urves for EGRET (red),
(blue), MAGIC (purple), all from [Funk
et al.
Fermi
2008℄, and the intended one for the
forthoming Cerenkov Telesope Array (CTA, violet) are shown. Right: Dierential
neutrino ux preditions from the inner region of M82, total and separated in dierent hannels. The neutrino preditions make use of the same explored parameters
already presented in the left panel and explained in the text.
68
Chapter 5. Starburst galaxies
value is set later on, in a reursive appliation of this model, as a t to radio data.
The same applies to other values, like the magneti eld. Together with the primary
eletron population, all the produed seondary eletrons are taken into aount
when omputing the steady state. For omparison, in Figure 5.2 (right), the steady
partile populations present in M82 are plotted together with the ones present in
NGC 253, from [Domingo-Santamaría & Torres 2005℄. The urves for eletron and
proton distribution display a similar behavior and level than those orresponding to
M82, emphasizing the similaritity of the initial harateristis of these two starbursts
as possible high-energy soures. With the steady eletron population determined,
a multi-frequeny spetrum (from radio up) an then be omputed and ompared
with experimental data.
Multifrequeny spetrum
Figure 5.3 shows the best math from this model:
a multifrequeny spe-
trum is overplotted to previous radio and IR data (see the aption for details).
At the lowest frequenies, radio data is no longer redued to the
entral starburst region.
Due to angular resolution of the observing instru-
ment, emission at this frequeny omes from the whole galaxy and annot
be separated from that oming only from the inner region.
Therefore, this
model ontribution is just a omponent of the total radiation below a few
108 Hz.
In the region of the spetrum where synhrotron emission dominates,
several parameters an be determined through repeated iterations: magneti
eld, EM, slope of proton injetion, and
Np /Ne
ratio.
In the range of un-
ertainty mentioned before, the lowest value for the magneti eld, 120 µG,
orresponds to the highest steady distribution (i.e., with the highest supernovae explosion rate assumed, and a value
Np /Ne = 30).
Inversely, a low
steady distribution implies the need for greater losses by synhrotron in order to math the data, thus pumping the magneti eld up to 290 µG. The
general t to observations is quite good in eah ase. These values of magneti eld are in agreement with previous results in [Völk
et al.
1989℄ and are
also similar to the ones found for the disk of Arp 220 [Torres 2004℄ or NGC
253 [Domingo-Santamaría & Torres 2005℄, as well as ompatible with measurements in moleular louds [Cruther 1988, Cruther 1994, Cruther 1999℄.
On the other hand, the slope of the proton injetion
p
is determined in this
step by mathing the orresponding slope for radio emission.
unertainties does not seem to aet
[Tabatabaei
et al.
p
The range of
signiantly.
2007℄ onrm, in a study of M33, that non-thermal emission
is spatially assoiated with star forming regions and propose that the ontribution of loalized strutures (SNRs) beome more important as the (synhrotron
photon) energy shifts to higher values. Although this may be true, the spatial
orrelation by itself is not really a proof of it, sine star forming regions also
have an enhaned osmi ray sea, and thus an inrease in the prodution of
seondary eletrons, whih emit non-thermally. In fat, [Bressan
et al.
2002℄
5.3. M 82
69
have shown that the ontribution of radio SNRs to the non-thermal emission
annot be dominant in galaxies, onluding that, for our Galaxy in partiular,
it annot be more than about 6%. In any ase, the unertainty in determining
the magneti eld in this model must be arefully taken into aount: most of
the radio emission is onsidered to ome from osmi ray eletrons that have
been either injeted by SNRs (primaries) or other aelerators, or produed
in osmi-ray interations (seondaries). If there is a ontribution to the total non-thermal radio signal made by unresolved SNRs, this would diminish
the estimation of the average magneti eld in the starburst. However, this
distintion annot be made with the data on M82 so far.
Regarding the far IR emission,
starbursts data generally require a dust
σ
emissivity law, ν B(E, T ), where typially
funtion. This greybody peaks at
∼45 K
σ = 1.5
and
B(E, T )
is the Plank
and has a luminosity of
(from [Teleso & Harper 1980℄ orreted by distane).
4 × 1010 L⊙
However, at higher
frequenies, a simple greybody emission annot explain observations, and
an exess appears at near IR wavelengths.
[Lindner 2003℄ proposed a dust
loud model in whih an envelope of dust grains surrounds a luminous soure.
Eah onentri shell dereases its density with inreasing radius and has
its own temperature and assoiated ux.
As a simpler but still aurate
approximation, an addition of just one seondary greybody is enough to t
the data well. The temperature of this greybody is warmer (T
the main one, and it has a smaller luminosity of
7×
≃ 200 K)
than
109 L⊙ . Small hanges
in the warm greybody luminosity or maximum of the peak are possible with
results similar to the ones presented here, and they have been explored. The
t to the IR data is quite good, as an be seen in Figure 5.3.
The model disussed in this work yields inverse Compton uxes of just
a few perent or less than the upper limits at X-ray energies,
[Persi
et al.
see e.g.,
2008℄ and referenes therein. The diuse emission is overwhelmed
by emission from ompat objets.
Gamma-ray preditions
Figure 5.4 shows the gamma-ray dierential ux that results from this model
oming from the entral region of M82, together with the sensitivity urves of
possible instruments observing it. The goodness of this predition is that it
is onsistent with the remaining range of the eletromagneti spetrum: the
partiles generating this emission, both hadrons and leptons, are the same
ones generating the radiation seen at lower energies. The model onrms that
there is not an expetation for detetion by EGRET, onsistent with EGRET
upper limit by [Torres
by [Cillis
et al.
et al.
2004℄, and the staking analysis of EGRET data
2005℄. Nonetheless, it predits M82 as a soure for
Fermi.
total ux estimations at high and very high energies are as follows:
The
70
Chapter 5. Starburst galaxies
•
for
E > 100 MeV, 2.6 × 10−8 (8.3 × 10−9 ) m−2 s−1 ,
•
for
E > 100 GeV, 8.8 × 10−12 (2.8 × 10−12 ) m−2 s−1 ,
with the parenthesis representing the results obtained with the lower energy
uto and lower supernova explosion rate. Separate ontributions are plotted
from eah gamma-ray hannel: neutral pion deay, bremsstrahlung and inverse
Compton (against CMB, far and near IR photon densities). Finally, Figure
5.4 also presents neutrino uxes oming from the inner part of the starburst
galaxy. The separate ontribution of eah neutrino proess an be seen, together with the total ux. As in the previous ase, parenthesis represent the
results obtained with the lower energy uto and lower supernova explosion
rate. The total ux estimations at high and very high energies are as follows:
•
for
E > 100 GeV, 1.2 × 10−11 (3.9 × 10−12 ) m−2 s−1 ,
•
for
E > 1 TeV 3.8 × 10−13 (9.9 × 10−14 ) m−2 s−1 .
Consequently, only if the highest end of the preditions happens to be a
realisti representation of the galaxy, the MAGIC telesope ould detet it
above 300 GeV with
5σ
in 50 h. Although the time required by MAGIC alone
would be unrealisti in order to obtain a detetion for the lowest end of the
preditions, with the upoming arrival of MAGIC II, the time to expend
on this soure ould be aordable.
The atual estimations for MAGIC II
sensitivity are a fator of 2 to 3 better than for MAGIC I, so the ux oming
from the starburst galaxy would be deteted within 50h. Similar estimations
would apply for the VERITAS array. But indeed, the instrument of hoie to
deeply study this soure would be the forthoming Cerenkov Telesope Array
(CTA). Presenting an instrument aeptane extending both to the lower
and higher energy ends ompared to the previous telesopes, with a 1 TeV
sensitivity one order of magnitude or more better than present Cherenkov
experiments, M82 should be a bright soure for CTA, if this model is a
realisti representation of this objet. With this observatory, studies on the
possible uto in the proton spetra ould be made, although M82 would still
look as a point like soure.
The dependene of these results on the initial injetion slope
p
has been ex-
plored by enforing the latter to be dierent. This dependee is not found to
be relevant, within a reasonable range. In Figure 5.5, this is shown by analyzing the preditions of the present model for a
−2.3
average injetion slope.
Both the multi-wavelength preditions in radio-IR and the gamma-ray emission are displayed. No relevant dierenes (within unertainties) are found in
the parameters that give rise to these urves.
Equipartition estimates
5.3. M 82
71
Figure 5.5: Comparison of the multi-wavelength preditions for dierent initial spetral slope in the injetion, see Figure 5.3 for further details. The blak urve orrespond to the model with proton injetion spetrum
p = 2.1
and magneti eld
B = 130µG, whereas the red urve orrespond to the results of modelling with
p = 2.3 and B = 170µG. The gamma-ray emission from the −2.3 model in the ase
of the highest SN explosion rate is shown against those obtained with the harder
injetion (the green shadow, oming from the unertainties desribed before). Main
dierenes appear at high energies.
It has already been mentioned that are should be exerised with equipartition
estimates and even more after the work done by [Bek & Krause 2005℄, where
2 may
it was shown that the usual formula to ompute the equipartition eld
be of limited pratial use.
This formula is based on the ratio
K
of the to-
tal energies of osmi ray protons and eletrons, whih is generally omputed
2
The equipartition eld is sometimes referred as the minimum-energy estimate of total magneti
elds strengths from radio synhrotron intensities
72
Chapter 5. Starburst galaxies
Figure 5.6: Dierent ontributions to the radio emission (synhrotron + free-free)
by the steady primary-only (blue) and seondary-only (yellow) eletron population,
also ompared to the total radio emission of the whole eletron population (blak).
without a full model of the system. In addition to other non-trivial tehnial
problems mentioned by Bek & Krause, if energy losses of eletrons are important, the number density between these partiles inreases with partile energy
and the equipartition eld may be signiantly underestimated. The orret
value an be omputed only by onstruting a model of gas density and osmi ray propagation. [Bek & Krause 2005℄ already emphasize that starburst
galaxies and regions of high star formation rate in the entral regions and
massive spiral arms of galaxies have high gas densities and mostly at radio spetra, thus non-thermal bremsstrahlung and other losses are important.
Sine the loss rate inreases linearly with gas density
ratio also inreases with gas density.
n, the proton-to-eletron
In addition, protons are also subjet
to energy-dependent losses or esape (e.g., diusion timesales dier). Thus,
the ratio
Np /Ne
depends really on energy, and any equipartition formula will
not ope. Using the steady population of relativisti partiles that have been
found as a result of this model, the energy ontent in suh omponent an be
determined. From this point, equipartition is
imposed
in order to see how the
magneti eld behaves. The obtained value is then ompared to the output
of the model. The result is 150 µG, whih is lose (but not the same) to the
estimation by [Weaver
et al.
2002℄, and of the same order as the magneti eld
from the model, 120 µG.
Neutrino preditions
[Loeb & Waxman 2006℄ have suggested that hadroni proesses in starbursts
an produe a large enough bakground of diuse high energy neutrinos to be
5.3. M 82
73
observable with the ICECUBE experiment. They arrive to this onlusion ritiized by [Steker 2007℄ starting, essentially, from two assumptions and
making order-of-magnitude estimations thereafter:
1. protons lose essentially all of their energy to pion prodution, and
2. a lower limit to the energy loss rate of the protons an be obtained from
the synhrotron radio ux, by assuming that all of the radiating eletrons
(and positrons) ome from pion deay.
Even
when
[Anhordoqui
photo-dissoiation
et al.
2008℄, the
in
1st
starbursts
is
a
minor
eet
assumption is arguable, as [Steker 2007℄
emphasized, beause partiles are subjet to diusion and onvetion by
winds in addition to pion losses, i.e., the galaxy is not a omplete alorimeter,
espeially at the highest energies.
The
2nd
assumption is arguable beause
synhrotron radiating eletrons are not only seondary partiles, but the
primaries too.
Figure 5.6 quanties this eet for M82 and ompares the
ontribution to the synhrotron radiation of the inner starburst if onlyprimary or only-seondary eletrons are onsidered.
to
∼ 100 GeV,
From
Ee − me ∼ 10−1
the seondary population of eletrons slightly dominates,
see Figure 5.2 (left), with the primary population ontributing signiantly.
Therefore,
it would not be very aurate to normalize the whole radio
emission to the seondaries alone (or primaries alone), and then use this to
x the energy loss rate of protons, from where one an estimate the neutrino
emission.
This study presents the rst full neutrino emission omputation
from a starburst galaxy whih is self-onsistent with the emission at all
eletromagneti frequenies inluded in the same model.
Given the detail
needed for suh a desription, a generalization of the present results for M82
to all the starbursts is not reommended. However, if this is done, and if it is
supported by basi assumptions on the starbursts number density within the
horizon, the neutrino diuse emission would be below the Waxman-Bahall
3
limit .
The
22,
sky-average
with
22
sensitivity
strings)
at
of
the
90%C.L.
1.3(2.0) ×
10−11 TeV−1 m−2 s−1
[Bazo Alba
et al.
urrent
to
a
(E/TeV)−2
ICECUBE
generi
E −2
depending
installation
ux
on
the
of
(IC-
νµ
is
analysis
2009℄. This is not enough to detet M82 diretly (see Figure
5.4). In fat, using the present estimation of the neutrino ux from M82 and
following the omments made by [Anhordoqui
et al.
2004℄, less than 2 events
per year would be expeted in the full ICECUBE faility. A more denitive
3
[Waxman & Bahall 1999℄ show that osmi-ray observations set a model-independent upper
bound of E2ν Φν < 2 × 10−8 GeV m−2 s−1 sr−1 to the intensity of high-energy neutrinos produed by
photo-meson (or pp ) interations in soures of size not muh larger than the proton photo-meson
(or pp ) mean-free-path. The bound applies, in partiular, to neutrino prodution by either AGN
jets or GRBs. This upper limit is two orders of magnitude below the ux predited in some popular
AGN jet models, but is onsistent with their preditions from GRB models. Their upper bound is
stated in eq. (3) and is illustrated in g. 1 [Waxman & Bahall 1999℄.
74
Chapter 5. Starburst galaxies
assessment of its sensitivity to suh a signal will need to await further renement of angular and energy resolutions, via improved knowledge of the
detetor response.
5.4 Disovery of HE and VHE emission from starbursts
5.4.1 Gamma-ray emission deteted from M82
Reently, VHE gamma-ray emission oming from M82 was laimed by VERITAS
[Aiari
et al.
2009a℄.
Meanwhile, the HE regime was overed by the
Fermi
tele-
sope, also deteting emission from the same galaxy in the rst year of observations
[Abdo
et al.
2010℄.
In Figure 5.7, this data is displayed, together with the spe-
tral energy distribution (SED) of the model presented in this Chapter. A separate
0
ontribution is shown oming from eah gamma-ray generator: neutral pion (π )
deay, bremsstrahlung and inverse Compton radiation.
The latter was omputed
having the osmi mirowave bakground (CMB), far and near infrared (IR) photon
densities as targets altogether, see Figure 5.8. The predition (green shade region)
is perfetly ompatible with the observational data presented both at HE and VHE,
within errors. The
Fermi
LAT and VERITAS data allow to further preise the orig-
inal preditions. Therefore, a range of parameters and some spei outputs (red
and blak solid urves) are explored to better onstrain the model to the observed
results, see Table 5.1.
As an be seen,
π0
deay ontribution dominates at VHE
energies.
5.4.2 NGC 253, onfronted with the model
The also near, barred-spiral starburst galaxy NGC 253 has been deeply studied through the years.
The distane has been subjet of unertainty, its value
ranging from 2.5 Mp [Turner & Ho 1985, Mauersberger
3.3 Mp [Mouhine
et al.
2005℄, 3.5 Mp [Rekola
et al.
et al.
1996℄, going up to
2005℄, and even 3.9 Mp, a-
ording to the detetion of the red giant branh [Karahentsev
et al.
2003℄.
Its
ontinuum spetrum peaks in the far IR, at about 100 µm, with a high luminosity of
4 × 1010 L⊙ ,
[Teleso & Harper 1980, Rie
et al.
1988, Melo
et al.
2002℄.
Its inner (100 p) region is haraterized, as well as M82, by starburst ativity
[Paglione
et al.
1996, Domingo-Santamaría & Torres 2005℄.
The integral ux published by H.E.S.S. onstrains previous preditions for NGC
253 at the VHE regime. Moreover, the rst results from the
Fermi
telesope add
more information to the spetrum of the galaxy at lower energies. A set of urves for
the SED are speially plotted in Figure 5.9 to ahieve this low ux, exploring the
unertainties in the distane to this galaxy and subsequent ranges in the magneti
eld and diusive timesale.
Apart from diusing away during
106−7 yrs
(see Table 5.2), partiles an esape
300 km s−1 ), and through
5
timesales of around a few 10 yrs.
the inner starburst onvetively, arried away by winds (∼
pion ollisions with ambient gas, in even shorter
5.4. Disovery of HE and VHE emission from starbursts
75
Table 5.1: Physial parameters used in the multi-wavelength model of M82, presented in the previous setion and in [de Cea del Pozo
et al.
2009b℄, together with
spei values that try to math the emission from the VERITAS detetion.
In
any ase, the (small) variations explored below are within the former preditions
of the original model. The list of parameters is divided in setions: observational
values, derived from observational values, obtained from modelling, and assumed.
SB stands for starburst.
Physial parameters
From 2009 model
Distane
Inlination
Radius SB
Radius Disk
Height SB
Gas Mass SB
Gas Mass Disk
(3.9± 0.3stat ± 0.3sys ) Mp
(77 ± 3)◦
300 p
7 kp
200 p
2 × 108 M⊙ (H2 )
7 × 108 M⊙ (HI),
1.8 × 109 M⊙ (H2 )
4 × 1010 L⊙
0.3 yr−1 (0.1 yr−1 )
1051 erg
10%
IR Luminosity
SN explosion rate
SN explosion energy
SN energy transferred
to CR
Convetive veloity
Dust temperature
Ionized temperature
Uniform density SB
Dust emissivity index
Emission measure
Magneti eld
Proton to eletron primary
ratio
Slope of primary injetion
spetrum
Emax for primaries
Diusion oeient slope
Diusive timesale
600 km s−1
45 K
10000 K
∼ 180 m−3
1.5
5 × 105 p m−6
120 µG (270 µG)
50 (30)
VERITAS-driven
model
...
...
...
...
...
...
...
...
0.2 yr−1 | 0.3 yr−1
...
10% | 5%
...
...
...
...
...
...
170 µG | 210 µG
...
2.1
...
106 GeV
0.5
1 − 10 Myr
...
...
...
76
Figure 5.7:
Chapter 5. Starburst galaxies
Energy distribution of the dierential gamma-ray uxes of M82, ex-
ploring a range of unertainties in supernova explosion rate and eieny to injet
energy from SN to CR. The shaded green area orresponds to the original model pre-
et al. 2009b℄. Data points and upper
and Fermi (diamonds) detetions.
sented in this Chapter and [de Cea del Pozo
limit orrespond to both VERITAS (stars)
5.5. Conluding remarks
Figure
5.8:
frared.
The observational data points orrespond to:
[Elias
et al.
Multifrequeny
77
1978℄ (irles),
spetrum
[Rieke
et al.
of
NGC
253
from
radio
to
in-
[Carilli 1996℄ (triangles),
1973℄ (asterisks),
[Ott
et al.
2005℄ (dia-
monds) and [Teleso & Harper 1980℄ (squares), and referenes therein. The results
from modelling orrespond to: synhrotron plus free-free emission (dashed), dust
emission (dotted) splitted in a ool (blue, Tcold = 45 K) and a warm (purple, Twarm
∼ 200 K)
omponent, and the total emission from radio and IR emission (solid).
The diusion timesale of the partile depends on the energy.
As the timesale
dereases, the slope of the gamma-ray spetrum beomes steeper (the losses are
higher).
The diusion oeient assoiated is
ompared to the
∼
∼ 1026−27 m−2 s−1
at
1 − 10 GeV,
1028 m−2 s−1 value in our Galaxy.
5.5 Conluding remarks
The multi-wavelength model presented in this Chapter explains reasonably well both
the HE and VHE emission oming from the two losest starburst galaxies M82 and
NGC 253, within a range of the explored parameters already mentioned. Every omponent of the emission an be traked to one and the same original CR population.
Moreover, this CR population results as a onsequene of all eletromagneti and
hadroni hannels from the primary and subsequently-produed seondary partiles.
CR enhanement present in these starburst galaxies is reeted in the high energy
density values that an be obtained from the steady proton population. Above a
proton energy of
(orresponding to Eγ ∼ 250 GeV), the energy density
−3 for M82 and similar value for NGC 253. Now that the VHE
∼ 1500 GeV
is around 10 eV m
78
Figure 5.9:
Chapter 5. Starburst galaxies
Energy distribution of the dierential gamma-ray uxes of NGC
253, exploring the unertainty in distane, a range of timesale diusion (τ0 )
and possible utos in the proton injetion spetrum.
The original model from
[Domingo-Santamaría & Torres 2005℄ is also shown for omparison, as well as data
points from
Fermi
detetion (diamonds) and the integral ux from the H.E.S.S.
detetion (square), transformed in dierential ux (assuming a range of injetion
spetra).
5.5. Conluding remarks
Table 5.2:
79
Physial parameters used in the multiwavelength model of NGC 253,
as presented both in the previous [Domingo-Santamaría & Torres 2005℄ study and
in this setion, but exploring some variations allowed within the model in order to
math the emission from the H.E.S.S. detetion. The list of parameters is divided
in setions: observational values, derived from observational values, obtained from
modelling, and assumed. SB stands for starburst.
Physial parameters
Distane
Inlination
Radius SB
Radius Disk
Height SB
Gas Mass SB
Gas Mass Disk
IR Luminosity
SN explosion rate
SN explosion energy
Convetive veloity
Dust temperature
Ionized temperature
Uniform density SB
Dust emissivity index
Emission measure
Magneti eld
Proton to eletron primary
ratio
Slope of primary injetion
spetrum
Emax for primaries
Diusion oeient slope
Diusive timesale
From 2005 model H.E.S.S.-driven
model
2.5 Mp
78◦
100 p
1 kp
70 p
3 × 107 M⊙
2.5 × 108 M⊙
(2 − 4) × 1010 L⊙
0.08 yr−1
1051 erg
300 km s−1
50 K
10000 K
∼ 600 m−3
1.5
5 × 105 p m−6
300 µG
50
2.3
106 GeV
0.5
10 Myr
2.6 Mp | 3.9 Mp
...
...
...
...
...
...
...
...
...
45 K
...
...
...
...
200 µG | 270 µG
30
2.1
...
...
1 Myr | 10 Myr
80
Chapter 5. Starburst galaxies
regime has been nally ahieved by ground-based telesopes, and
that detetions are possible from lower energies (∼
of gamma-ray emission is begining to appear.
Fermi
has proven
100 MeV), a full and lear piture
PART II:
Observations using the MAGIC experiment,
and simulations of future observations using CTA
Chapter 6
Analysis of MAGIC data
Contents
6.1 Cherenkov tehnique and telesopes . . . . . . . . . . . . . . 83
6.1.1
Cherenkov light . . . . . . . . . . . . . . . . . . . . . . . . . .
84
6.1.2
Hadroni and eletromagneti showers . . . . . . . . . . . . .
85
6.1.3
Imaging Air Cherenkov Tehnique . . . . . . . . . . . . . . .
86
6.2.1
Struture and reetor . . . . . . . . . . . . . . . . . . . . . .
88
6.2.2
Camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
89
6.2.3
Readout, trigger and data adquisition . . . . . . . . . . . . .
90
6.2.4
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . .
91
6.2.5
Observation modes . . . . . . . . . . . . . . . . . . . . . . . .
91
6.3.1
Mono observations . . . . . . . . . . . . . . . . . . . . . . . .
96
6.3.2
Stereo observations . . . . . . . . . . . . . . . . . . . . . . . .
100
6.2 The MAGIC telesopes . . . . . . . . . . . . . . . . . . . . . . 88
6.3 Analysis method . . . . . . . . . . . . . . . . . . . . . . . . . . 91
The atmosphere bloks most of the radiation that arrives to Earth, whih otherwise would be harmful for life. In Astronomy, this implies that most of the observations above ultraviolet (UV) radiation, for instane, need to be arried out
from spae.
However, the atmosphere an also at as a alorimeter and thus al-
low the indiret detetion of very energeti partiles, osmi and gamma rays. The
MAGIC (Major Atmospheri Gamma-ray Imaging Cherenkov) telesopes, among
other ground-based experiments, prots from this irumstane using the Cherenkov
tehnique.
6.1 Cherenkov tehnique and telesopes
Cosmi rays that arrive to Earth ollide with the nulei present in the atmosphere.
The seondary partiles produed interat again with other atmosperi nulei, generating a asade of partiles, also dened as EAS, extended atmospheri showers,
[Longair 1992℄. This ollision proess ontinues, losing energy in eah step, until the
ritial energy for reating partiles is reahed. By the time the radiation arrives to
the ground level, it an be deteted by imaging atmospheri Cherenkov telesopes
(IACT) as Cherenkov light.
84
Chapter 6. Analysis of MAGIC data
Figure 6.1:
v < c/n,
Polarization of the medium by a harged partile with (a) low veloity,
and (b) high veloity,
v > c/n.
Huygens onstrution of Cherenkov
wavefront in ()
6.1.1 Cherenkov light
The Cherenkov eet ([Cherenkov 1934℄, [Tamm & Frank 1937℄) takes plae when
a harged partile travels at a speed larger than in a transparent medium
(v
= βc, β > 1/n),
disrupting the loal eletromagneti eld.
The light emission
results from the re-orientation of the instantaneous eletri dipoles indued by the
partile in the medium. When the distortion travels faster than the generated photons, the wavefronts along the trajetory an sum oherently (aording to Huygens
onstrution, see Figure 6.1) and, if the medium is transparent, the light propagates
at an angle
θc :
cosθc =
1
.
βn
(6.1)
The energy threshold for the harged partiles to emit Cherenkov light is:
where
m0
Eth = q
m0 c2
=p
2
1 − βmin
m0 c2
1 − 1/n2
(6.2)
is the rest mass of the partile.
The number of Cherenkov photons emitted per trak length by a harged partile
is given by [Yao
et al.
2006℄:
d2 N
2παZ 2
=
dxdλ
λ2
where
α
is the ne struture onstant.
1
1−
(βn)2
(6.3)
From this equation, it appears that
most of the Cherenkov photons are emitted at short wavelenghts and their number
6.1. Cherenkov tehnique and telesopes
Figure 6.2:
Sheme of a
85
γ -ray indued eletromagneti shower (right) and a hadron-
indued shower (left) developing in the atmosphere
dereases when going from ultraviolet to optial light.
The main soure of atten-
uation (between 15 and 2 km above sea level) is the Rayleigh sattering, in whih
photons are sattered by polarizable air moleules with a smaller size than the photons wavelenght.
Another important ontribution omes from the Mie sattering,
produed when photons interat with small dust partiles suspended in the air. Finally, Cherenkov photons an be absorbed by the ozone layer (for
λ < 290 nm)
in
the upper part of the atmosphere.
The previously dened Cherenkov angle
the altitude.
θc
an be expressed as a funtion of
Sine the refration index is not onstant in the atmosphere, the
relationship is suh that
θ
inreases with dereasing height.
Therefore, when the
light emitted at dierent heights reahes the ground, a light pool is reated: the
photons arrive at a similar distane from the axis of the shower of partiles, and the
projeted ones of light that should be rings beome smeared out. The Cherenkov
light density is onstant up to 120 m away from the shower axis, where the sudden
drop ours.
6.1.2 Hadroni and eletromagneti showers
In order to produe this Cherenkov light, very energeti osmi and gamma rays are
needed. Depending on the nature of the primary partile, the development of the
shower an be very dierent (i.e., Figure 6.2).
If the primary partile is a gamma-ray, the asade will be an eletromagneti
one. When a photon interats with one atmospheri nuleus, an eletron-positron
pair is generated. These seondary partiles loose energy produing less energeti
photons through bremsstrahlung.
The shower keeps developing, quite symmetri-
86
Chapter 6. Analysis of MAGIC data
ally, alternating between pair prodution and bremsstrahlung, until a ritial energy is reahed, 83 MeV, below whih the main energy loss is due to ionization.
This point (usually between 7 and 13 km above sea level) oinides with the shower
maximum, and after that, the asade dies out.
involved, the partiles from a
γ -indued
Due to the relativisti energies
shower are strongly olimated along the
inident diretion.
On the other hand, when osmi rays (usually protons) hit the atmosphere, many
dierent proess and types of seondary partiles are involved. These hadroni asades an generate pions (90%), kaons and antiprotons (10%) when interating
with atmospheri nulei, and in subsequent steps, muons and neutrinos, among
other partiles. The hadroni ore of the shower ontinues to interat until the energy threshold for pion prodution is reahed (1 GeV), then the ionization proess
beomes dominant and the asade dies out. The majority of seondary partiles
are pions, and therefore an initiate an eletromagneti sub-shower. In their neutral form, those pions deay mainly in two photons.
muons and neutrinos.
The harged pions deay in
The latter will not interat due to their low ross-setion,
whereas muons interat almost exlusively through ionization and, thanks to their
long lifetimes, usually reah the ground before deaying. Hadrons are able to transfer
signiant momenta to the seondary generated partiles, thus widening the tranverse evolution of the shower. Another important harateristi is that the arrival
diretions for the hadroni showers are isotropi, ontrary to
γ -indued
showers,
whih originally ome from the pointed astronomial soure. These, together with
morphologial and timing dierenes, are important features when disriminating
gammas from hadrons deteted with IAC telesopes.
6.1.3 Imaging Air Cherenkov Tehnique
The goal of the imaging air Cherenkov (IAC) telesopes is to detet, at ground
level, very energeti photons oming from astronomial objets, using the Cherenkov
eet.
These telesopes ollet Cherenkov light on a reeting surfae (mirror)
and fous it on a detetor (amera). The detetor's instrumentation onverts the
photons into eletri pulses and later saves these as a geometrial projetion of the
atmospheri showers.
The image of the air shower is the key of the IAC tehnique. It ontains information about the longitudinal development of the asade of partiles through the
number of photons and arrival time of the images. Cherenkov photons emitted at
dierent heights reah the amera at dierent positions, see Figure 6.3. When pointing to a possible
γ -ray soure, the most energeti seondary partiles (loated at the
top of the shower) will hit losely to the entral part of the amera. Meanwhile, the
less energeti lower part of the shower will form images away from the enter of the
amera. The amount of deteted Cherenkov light is an estimator of the total number
of seondaries, and therefore, of the energy of the primary partile. Moreover, the
orientation and shape of the image of the shower is a good indiator of the inoming
diretion and the nature of that primary partile.
For instane and as explained
6.1. Cherenkov tehnique and telesopes
87
Figure 6.3: Image formation sheme in the amera of an IAC telesope. The values
are referred to a 1 TeV
γ -indued
shower. The blue part is the image head whereas
the red part is the image tail. The numbers in the pixels orrespond to the number
of inident photons. [Tesaro 2010℄
88
Chapter 6. Analysis of MAGIC data
in 6.1.2, arrival diretions of the hadroni showers are uniformly distributed along
the detetor and their projeted image is wide spread, while
γ -ray
shower images
have nie elliptial shape and their axis point to the enter of the amera.
This
morphologial dierenes help rejeting hadroni events from the bakground.
In order to extrat
γ -ray indued showers from the bakground, an energy thresh-
old is imposed to the primary photon:
Eth ∼
r
φΩτ
εA
(6.4)
The energy threshold is inversely proportional to the square root of the quantum
eieny of the detetor (ε) and the mirror surfae (A). It also depends on the solid
angle subtended by the mirror (Ω), the integration time of the signals in the amera
(τ ) and the bakground light from the night sky (φ, whih main soures are stars,
airglow, zodiaal light, artiial man-made light or even moon light).
Therefore,
IAC telesopes need large mirror surfaes and high sensitivity photodetetors.
6.2 The MAGIC telesopes
Sine the fall of 2009, the MAGIC experiment, seen in Figure 6.4, observes gammaray soures with two 17-m diameter IAC telesopes.
They are loated at the
Observatorio del Roque de los Muhahos, in La Palma, Canary Islands, Spain
◦ N 17◦ W , 2200m above sea level). Their design mainly fullls two aims: ahiev-
(28
ing the lowest energy threshold (of 50 GeV for standard observations, or even 25
GeV with a speial trigger setup), and a fast repositioning (an average of 30 seonds
takes to point the telesopes from one point to another in the sky).
The earliest
operations started in 2004 with one single-dish telesope (MAGIC-I), and lately the
instrument was upgraded to stereosopi observing mode by adding a seond - in
many ways, lone - telesope (MAGIC-II) at
∼ 85 m
from the rst one. In doing
so, the system improved the sensitivity, the primary energy reonstrution and the
soure position determination.
A list and desription of the harateristis of the
MAGIC experiment is presented in the following setions.
6.2.1 Struture and reetor
Light arbon ber reinfored tubes support the struture of both telesopes and
allow for a fast repositioning in any diretion of the sky, for instane, in ase of
gamma-ray burst (GRB) alerts.
The drive system also provides a high degree of
pointing auray. Eah telesope has two motors of 11 kW of power eah in the
azimuth axis and one for the zenith movement. The mentioned pointing quality is
reinfored with a starguider system.
It onsists on a CCD amera plaed at the
4.6◦
eld of view (FOV), thus imaging partially the
amera and a portion of the sky.
Using six LEDs on the amera as a referene
enter of the reetor, with a
system, the starguider ompares the position of deteted stars with a atalogue. In
6.2. The MAGIC telesopes
89
Figure 6.4: Piture of the two MAGIC telesopes: MAGIC-I (left) and MAGIC-II
(right)
this way, orretions for possible mispointing an be later applied during the analysis
of the data.
The reetor has a paraboli urvature in order to minimize the arrival time
spread and improve the signal to noise ratio.
As it was previously stated, both
telesope dishes have 17 m of diameter, with a total reetive surfae of 239 m
(80 − 85)%
2 and
of reetivity in the range from 250 to 650 nm. MAGIC-I has 49.5 m
49.5 m spherial mirrors, while MAGIC-II has 1 m
doubles the size of the former.
×
×
1 m mirror elements, whih
Despite the rigidity of the struture, the reetor
surfae an suer distortions depending on the pointing position of the telesopes,
therefore a re-adjusting needs to be done by the ative mirror ontrol (AMC). Eah
mirror panel has a laser at the enter and two mehanial atuators.
A amera
reords the image formed by the lasers when pointing to the losed amera, and the
alignment of the mirrors is ompleted via software orders to the motors.
6.2.2 Camera
The amera reeives the Cherenkov light, olleted in the reetor surfae, and
onverts the signal into photoeletrons.
attempts to have a large FOV (∼
gamma/hadron separation).
sopes are slightly dierent.
The design of the amera is suh that it
3.5◦ ) and a ne pixelization (to improve the
Photomultiplier tube (PMT) ameras for both teleIn the ase of MAGIC-I, it has hexagonal shape
and onsists of 397 small (30 mm diameter) inner PMTs, surrounded by 180 big-
90
Chapter 6. Analysis of MAGIC data
Figure 6.5: Sheme for the standard trigger onguration in MAGIC I (left) and II
(right) ameras ([Meui
et al.
2007℄, [Cortina
et al.
2009℄).
ger (60 mm diameter) PMTs. Meanwhile, MAGIC-II amera has a irular shape
and 1039 medium (25 mm diameter) PMTs.
To improve the quantum eieny
(QE) and ompensate the dead spae between the edges of the rounded PMTs, eah
one is surrounded by hexagonal-shaped, non-imaging light onentrators (Winston
Cone); in addition, the hemispherial entrane window is oated with a milky laquer doped with a wavelenght shifter. Temperature and humidity inside the amera
are ontrolled by a water ooling system.
6.2.3 Readout, trigger and data adquisition
All the eletronis of the MAGIC system are kept in a faility 150 m away from
the telesopes, in order to avoid extra weight to the amera and keep it safe from
bad weather onditions. The eletroni signal is onverted into an optial one and
travels from the amera to the readout system via optial bers. When the signal
is reeived, it is transformed into an eletri urrent by means of a photodiode,
and split in two signals. One part is digitized with a multiplex 2GSamples/s Flash
Analog-to-Digital-Converter (FADC) and kept in a ring buer for MAGIC-I. For
MAGIC-II, the Cherenkov pulses are sampled by low-power Domino Ring Sampler
hips, working at 2GSamples/s, and stored again in a ring buer. The other part
of the eletroni signal is sent to the trigger system.
Only a ertain -inner- region of eah amera (see Figure 6.5) is onsidered for
the trigger, whih in turn has dierent deision levels.
The rst level (L0T) is a
disriminator: if the analog signal of one pixel exeeds a ertain threshold (whih
depends on light onditions), the hannel signal goes to the next level.
For L1T,
if lose paked next-neighbour (3, 4 or 5 NN) pixels have a signal in a short (2
5 ns)
−
time window, the harge is reorded (in mono-observations). There is a L2T
that would allow further online pattern reognition later in the analysis, but it has
not been implemented. The atual standard mode of operation, i.e., stereosopi,
requires a L3T: if the signal is deteted at both telesopes in a ertain time window,
6.3. Analysis method
91
then the events are reorded.
For some dediated observations (like pulsar observations), there is another option, alled the analog sum trigger [Aliu
et al.
2008a℄, that lowers the energy thresh-
old down to 25 GeV. It onsists of a linear sum of the signals of large pathes of
pixels. This time, the trigger area is not an inner irle but a entered doughnut
shape.
In ase the trigger ours, the digitization proess stops and the information
ontained in the ring buers is kept in a dis. The raw data are stored by the data
adquisition (DAQ) system in run les of 2GB maximum. All les are transferred to
the data enter Port d'Informaio Cientia (PIC, htt://magi.pi.es) in Barelona.
6.2.4 Calibration
An optial alibration system is needed to determine how to onvert FADC ounts
into a number of photoeletrons (phe). In order to ahieve this, a set of dierent
LEDs (emitting at 370, 460 and 520 nm) are red onto the amera to uniformly
illuminate it.
When the signal is triggered, the alibration events are reorded
in dediated runs, and an be later used in the analysis hain to orret for gain
variations.
6.2.5 Observation modes
The MAGIC telesopes an observe in two modes:
one hand, to observe a soure in
on-o
on-o
and
wobble.
On the
mode, the telesopes rst point to soure
position in the sky (ON), and then, to a dark region of the sky (with no-known
gamma-ray soure and similar zenith and general onditions), in order to substrat
the bakground (OFF). On the other hand, if the
wobble
mode [Fomin
et al.
1994℄
is hosen, two opposite diretions in the sky, 0.4 degrees away from the soure, are
observed during 20 minutes eah. For
wobble
mode observations, the ON region is
dened around the soure position in the amera, while the OFF region is entered
at a position opposite to the soure with respet to the amera enter (so-alled,
the anti-soure position). The standard MAGIC analysis uses also two additional
OFF regions orresponding to the soure position rotated by
±90◦
with respet to
the amera enter, see Figure 6.6. The standard observation mode in MAGIC is the
wobble
mode beause, despite the lower sensitivity, it saves observation time and
provides a better bakground estimation.
6.3 Analysis method
The nal goals of the data analysis software of a ground-based Cherenkov telesope
are:
distinguishing between gamma-like and bakground-like events, determining
the energy of the primary
γ -ray
(to derive the energy spetrum of the deteted
emission), alulating the inoming diretion of the gamma shower to estimate the
92
Chapter 6. Analysis of MAGIC data
Figure 6.6: Sketh of the denition of the signal (ON) and bakground (OFF) regions
in
wobble
observations. The anti-soure is the OFF position loated symmetrially
to the ON position (the red irle) with respet to the enter [Mazin 2007℄.
6.3. Analysis method
93
position of the emitting soure, and determining the arrival time of eah
γ -ray
andidate to produe light urves.
In this setion, the analysis tehnique used in MAGIC will be desribed in detail. The MARS software pakage (MAGIC Analysis and Reonstrution Software,
[Moralejo
et al.
2009℄) is a olletion of programs for the analysis of the MAGIC
data, written in C++, in the ROOT framework maintained at CERN. Eah program orrespond to a ertain step in the analysis proedure:
• allisto :
• star :
performs the signal extration and alibration steps.
arries out the image leaning and alulates the image parameters.
• osteria :
• melibea :
is in harge of the training of the Random Forest.
applies the trained matries to alulate the
hadronnes
parameter
and the estimated energy of eah event.
• uxl :
alulates the energy spetrum, the eetive area and the light urve
of the soure.
• elestina/aspar :
produes a skymap of the exess events of the region of the
sky that ontains the soure.
The reonstrution of gamma ray initiated air shower harateristis requires
detailed Monte Carlo (MC) simulations of the shower development and of the response of the telesope. In the MAGIC analysis, MC gamma showers are also used
to optimize the uts for bakground rejetion and to estimate the eetive olletion area after all uts, whih allows onverting exess events into a physial ux of
γ -rays. The MC simulation program
[Hek et al. 1998℄. Gamma showers
of MAGIC uses the software CORSIKA 6.019
are simulated, under the US standard atmo-
sphere, and the output Cherenkov photons that arrive to ground level are reorded.
As a seond step, the so-alled
reetor
program rst omputes the Cherenkov light
attenuation in the atmosphere, and subsequently, the reexion of the photons on
the dish mirrors is simulated.
Next, the
amera
program simulates the response
of the telesope PMTs and both trigger and DAQ systems.
Camera
also performs
a smearing of the arrival diretions aording to the optial point spread funtion
(PSF) of the telesope. After this point, the simulated events are ready to be used
in the MAGIC analysis hain. In the present Thesis, analysis of soures observed
in both mono and stereo mode are presented. The analysis hain is introdued in
what follows.
Signal extration and alibration
The Cherenkov photon ashes produe very short signal pulses when they
reah the PMTs, whih are digitized and stored in the raw data.
The re-
onstrution of this information is alled signal extration. One the number
of ounts is reovered, the alibration onsists in onverting these into number of photoeletrons (phe). Thus, dediated alibration les are reorded as
94
Chapter 6. Analysis of MAGIC data
explained in 6.2.4 (see also [Gaug 2006℄). Up to this point, analyzers an obtain this information diretly from the data enter at PIC, without personally
running the programs or exeutables.
Image leaning
At this stage, pixels whih ontain no signal from the gamma showers are
reognized and eliminated.
Only the shower image survives.
The standard
method leans the image in two steps: rst, it selets groups of at least two
pixels (ore ) with a phe ontent higher than a minimum value
sorrounding it (boundary ) an be added if they exeed a
also have at least another boundary pixel exeeding
q2 .
q1 , then, pixels
signal q2 and if they
Next, the mean arrival
time of all ore pixels is alulated. Only those ore pixels inside the timing
oinidene window (δt1 ) are kept, and similarly (δt2 ) for the boundary pixels.
The usual image leaning setting used in MAGIC-I analysis has
q2
= 3 phe,
δt1
= 4.5 ns and
δt2
= 1.5 ns [Oya 2010℄.
q2
= 6 phe,
When arrival time
information is not used, a harder image leaning is applied (e.g.
and
q1
q1
= 10 phe
= 5 phe, whih is the one used in MAGIC-II).
Image parameters
The leaned images an be haraterized by the so-alled Hillas parameters
[Hillas 1985℄, that are related to the statistial moments of the images up to
third order.
For a graphial interpretation of some of these, see Figure 6.7.
The following parameters are independent of the position of the soure in the
amera:
• SIZE:
Total number of phe in the image. It is roughly proportional to
the primary partile energy for a xed impat parameter (distane of the
shower from the telesope axis, a.k.a. IP) of the shower.
• LENGTH: Seond moment of the light distribution along the major image
axis.
• WIDTH:
Seond moment of the light distribution along the minor image
axis.
• CONC[N℄:
Fration of the total amount of phe ontained in the N most
luminous pixels. Usually, N = 2.
• leakage:
Fration of the light of the image ontained in pixels that belong
to the outermost ring of pixels of the amera. It is useful for reognizing
images partially outside the amera.
• M3Long:
Longitudinal third moment of the distribution of the harge
along the major axis. It is used to resolve the head/tail degeneray.
• time RMS:
It is the RMS of the arrival times of all pixels that survived
the image leaning, and measures the time spread of the arrival times.
The following image parameters are dependent on the position of the soure
in the amera:
6.3. Analysis method
95
Figure 6.7: Graphial representation of some of image parameters desribed in the
text. The nominal position of the observed soure is (x0 , y0 ) [Mankuzhiyil 2010℄.
96
Chapter 6. Analysis of MAGIC data
• alpha:
Angle (α) between the diretion of the major axis and the line
onneting the image entroid with the soure position.
γ -ray
• Dist:
showers from the soure will have small
alpha
Images from
values.
Distane between the image entroid and the soure position in the
amera. It is orrelated to the impat parameter of the shower.
• time gradient:
It measures the magnitude of the time prole of the event.
This parameter is obtained from the slope of the linear t applied on the
arrival time versus the spae oordinate along the major axis.
Note that the time-related image parameters are not exatly Hillas parameters, but are used to enhane the analysis performane [Tesaro
[Aliu
et al.
2009℄. There is also another parameter,
Disp,
et al.
2007℄,
that allows to pro-
due sky-plots even with a stand-alone Cherenkov telesope and will be introdued in 6.3.1.
Quality seletion
Sine observations with a Cherenkov telesope are performed under partially
ontrolled onditions, data quality seletion uts need to be done before starting the analysis of any astronomial objet. The most reliable and eetive
parameter is the trigger rate. Sine the CR ux is dominated by the onstant
isotropi hadron bakground, the trigger rate is expeted to be onstant during
the observation time. Therefore, a ut on the event trigger rate is an eetive
quality ut to avoid, for instane, bad weather onditions like louds or dust
in the air (alima ).
A typial MAGIC analysis usually inludes a few hours of observation of the Crab
Nebula soure. These observations are hosen as lose as possible to the observation
period and zenith angle of the analyzed soure. Given the strong and steady signal
from the Crab Nebula (onsidered a standard andle in
γ -ray
Astronomy), these
data are onsidered as a test sample where to hek the onsisteny and sensitivity
of the urrent analysis.
6.3.1 Mono observations
The tasks that are going to be explained below try to estimate the main harateristis of the primary partile that originated the air shower: the nature, energy and
diretion of the primary
and
melibea.
γ -ray.
The orresponding programs in MARS are
osteria
Bakground rejetion
In order to disriminate images of gamma showers from the muh more abundant images of hadroni origin, as well as those from isolated muons and utuations of the night sky bakground, previously desribed image parameters
are used (also others like the zenith distane). MAGIC analysis makes use of
the
Random Forest
(RF) method for this task. The RF method uses a
forest
6.3. Analysis method
Figure 6.8: Sketh of a
97
tree
struture for the lassiation of an event
length and width. The deision path through the
tree,
v
via size,
leading to lassiation of
the event as hadron an be followed [Errando 2009℄.
of deision
trees
to lassify eah event. The deision
from MC simulated
γ -ray
trees
are reated (trained)
events and real events from hadron events from un-
altered data samples (sometimes, also o-data samples). The individual
trees
are grown by using a list of image parameters with a proven disrimination
power and nding adequate uts on these parameters (see Figure 6.8). From
the training sample, a binary deision
tree
an be onstruted, subdividing
the parameter spae in two parts, and iteratively repeating the proess. The
proedure stops when a sub sample omposed only by gammas or by hadrons
is found (a
leaf
of the
tree
is reahed).
The ending
leaf
is labeled as a 0
(gamma) or 1 (hadron).
The bakground rejetion takes plae after the training. Eah event is passed
through all deision
leaf
tion
trees
and they will sore 0 or 1, depending on the reahed
label. A mean sore is omputed averaging over all the dierent separa-
tree
results. This average is alled
hadronness
(h) and represents a sort
of probability for the event to be a hadron (h lose to 1) or a gamma (h lose
to 0). There are two kinds of parameters used to train the h parameter: pa-
γ s (WIDTH,
LENGTH, CONC, Dist, M3Long, time RMS and time Gradient ) and, also,
SIZE and zenith distane beause the rest of parameters depend strongly on
rameters whih have power to disriminate between hadrons and
the size of the shower images. Inluding these last two, the uts in RF an be
saled dynamially with the geometry of the shower image.
Energy reonstruion
The energy of the
γ -ray
events is also reonstruted by the Random Forest
98
Chapter 6. Analysis of MAGIC data
method, using training MC
with a known primary
γ -ray
samples.
A MC simulated
γ -ray
γ -ray energy is filled in bins of logarithmi
sample
energy. The
lassier will be trained to aommodate eah event in a partiular energy
bin.
After this, eah tree will assign a speifi energy range to eah event,
hadronness parameter. The
WIDTH, LENGTH, SIZE, log(SIZE/(WIDTH
LENGTH)), CONC, leakage, ZD, Dist and time Gradient, being the last two
soure position dependent. The obtained energy resolution is about 20% for
that will be analogous to the previously desribed
parameters used normally are
energies from 100 GeV to 10 TeV, inreasing at lower energies and dereasing
for higher ones.
The energy of the
γ -rays
is usually overestimated at low
energies (<100 GeV) and underestimated at higher energies (>10 TeV). The
finite resolution and bias require that the energy estimation is later orreted
by the spetrum unfolding, using a migration matrix.
Analysis approahes (α and θ2)
The analyzer an either deide to go for an
square-type analysis.
rameters.
Theta, (θ ),
Alpha
alpha -type
analysis or a
theta -
has already been desribed with the image pa-
is the angular distane in the sky between the expeted
emitting position and the reonstruted inoming diretion of the reorded
shower. An exess of events at small values of
alpha
or
θ2
is expeted, as the
γ -ray shower images will be oriented towards the enter of the amera. The
alpha -analysis approah is suitable when the emitting soure an be onsidered as point-like. If the point-like soure has very well known sky oordinates
a soure-dependent analysis an be performed:
a priori assumptions about
the loation of the soure are done. The advantages are that, by using some
extra image parameters (like
M3long
or the
time gradient ),
a better bak-
ground rejetion and an enhaned sensitivity in the analysis are ahieved.
The
θ 2 −analysis
is, instead, more suitable when the soure of gamma rays
is extended or when the position of a point-like soure is not well known. A
soure-independent analysis allows the prodution of sky maps showing the
exess of gamma rays in the observation eld, but no assumptions about the
soure loation are done, resulting in a less sensitive analysis. In the ase of
a single dish telesope, the reonstrution of the primary gamma diretion is
done through the so-alled
Disp
method.
One this step of the analysis is reahed, the signal may have been found as
arriving from the pointed soure. If the signal is strong enough, both a spetrum
and a light urve an be alulated with
uxl.
If it is not statistially meaningful,
dierential or integral upper limits on the gamma-ray ux an be set. There is also
the possibility of produing a skymap, by projeting the arrival diretions of the
seleted gamma-ray andidates into elestial oordinates.
Spetrum
The dierenial energy spetrum of a soure is dened as the number of
arriving to Earth, per unit of energy, time and area:
γ -rays
6.3. Analysis method
99
dNγ
dF
=
dE
dtdAef f dE
Nγ
Here
(6.5)
γ -rays and t the exposure time. The
Aef f , is the area in whih air showers an be observed
is the number of deteted
eetive olletion area,
by the telesope, folded with the effiieny of all the uts applied in the analysis
(εγ ). It inreases with the zenithal angle (speially above 45 degrees). This
ut effiieny an be estimated using MC gamma rays, and is defined as the
number of produed gammas divided by the number of events that survive the
analysis uts. Loose bakground rejetion uts are applied in order to ompute
the spetrum beause they redue the eet of systemati unertainties and
provide larger statisti of exess events.
Due to the nite resolution of the detetor and the bias introdued in the
energy estimation, the measured spetra beome distorted.
The unfolding
proedure tries to orret this distortion. Those biases are due to the fat that
the true energy of the inoming gamma-rays is not measured but indiretly
estimated. Several unfolding methods an be hosen in the MAGIC analysis,
differing from the algorithm used for the alulation of the true distribution
[Albert
et al.
2007℄. An agreement within the different methods is required
to trust the obtained results.
The
light urves
are plots where the integral gamma-ray ux above a ertain
energy is shown as funtion of the observation epoh. Cuts used for the
urve
light
are the same as for the spetrum alulation.
Skymap
As mentioned previously, sky maps are alulated by reonstruting the
arrival diretions of the gamma-like showers in amera oordinates and
projeting them into elestial oordinates.
gamma-ray images is estimated using the
[Domingo-Santamaría
et al.
Disp
The arrival diretion of the
method ([Lessard
et al.
2001℄,
2005℄). The method assumes that the arrival di-
retion of the primary partile lies on the major axis of the shower. The
Disp
parameter is dened as the angular distane between the reonstruted soure
position in the amera and the enter of gravity of the shower image.
parameterization used to alulate
Disp
The
is optimized using a MC gamma-ray
sample, and is a funtion of the image parameters. One important degeneray
in the
Disp
method are the two solutions found for a soure loation: one in
the head of the image and another in the tail. The
M3long
parameter is used
to hoose and plae the soure position always loser to the head of the image.
elestina. It produes sky
methods, on-o, wobble and model,
The program used to perform skymaps is alled
plots with three bakground estimation
depending on the observation mode (the latter serves for both). Reently, two
elestina : aspar and zin. Zin is to the
aspar is to the elestina wobble skyplots. In
-simpler- programs have replaed
elestina
model skyplots what
100
Chapter 6. Analysis of MAGIC data
the present work, when observations in wobble mode are presented,
aspar
is the hosen program to reprodue skymaps, and the bakground estimation
was done from the same data set.
elestina
However, in one set of observations, the
program has been used (on-o observations, see next Chapter for de-
tails), due to the fat that
zin
was still not available at that moment. After
the bakground is built, a map of exess events is generated by subtrating the
distribution of bakground events to the
γ -ray
andidates. The exess map is
smoothed using the PSF of the telesope.
6.3.2 Stereo observations
Sine fall 2009, MAGIC-II has joined its twin Cherenkov telesope MAGIC-I in the
observing duty.
The two telesopes an be operated independently or in stereo-
sopi mode. The stereosopi mode leads to a better reonstrution of the image
parameters and a stronger bakground suppression. When an image of the shower is
obtained with the two telesopes, image parameters are individually obtained from
the signal of eah telesope, and then ombined to alulate stereo parameters. The
inoming diretion of the shower (i.e., the soure position) is obtained from the intersetion of the major axes of the two images of the shower. In addition, the height
of the shower maximum an also be estimated.
The stereo analysis, therefore, uses the
θ 2 -approah as the standard one.
The rest
of the hain onsists basially on dupliating eah step: two alibration, two random
forests and two star les are generated, both for the data and the MC. After that, a
new program alled
SuperStar
is used to onvert two star les with individual-image
parameters to a Stereo-Parameter le. It performs the stereosopi reonstrution of
the shower parameters (diretion, ground impat, altitude) and an also reonstrut
the energy from look-up tables. Then, modied versions (to make use of the stereo
parameters) of
melibea, uxl
and
aspar/zin
omplete the analysis method.
Chapter 7
Two Milagro-deteted, Bright
Fermi Soures in the Region of
SNR G65.1+0.6
Contents
7.1
7.2
7.3
7.4
7.5
7.6
Motivation . . . . . . . . . . . . . . .
Observations . . . . . . . . . . . . . .
Data analysis . . . . . . . . . . . . . .
Upper limits on the gamma-ray ux
Interpretation and disussion . . . .
Conlusions . . . . . . . . . . . . . . .
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101
103
104
106
109
110
7.1 Motivation
Sine the launh of the
Fermi
satellite and the publiation of new soure list, several
proposals were presented by the dierent IAC telesope ollaborations to arry out
Fermi
above 100
a follow up of these soures up to the highest energies. In February 2009, the
ollaboration published a list of the most signiant gamma-ray soures
MeV, deteted by the large area telesope (LAT) within 3 months of observation
[Abdo
et al.
2009℄. Among the galati soures deteted by LAT, 34 were within
the eld of view of the Milagro gamma-ray observatory ([Abdo
referenes within).
10 − 50 TeV.
with ondene levels above
Fermi
2009i℄ and
Consequently, the Milagro ollaboration re-analysed their previous
skymap looking for ounterparts [Abdo
with
et al.
The sensitivity of this instrument peaks in the energy range
3 σ.
et al.
2009i℄, and laimed 14 new soures
Sine many of them were positionally oinident
pulsars, they are mostly believed to be Pulsar Wind Nebula (PWN), or
similar soures.
The MAGIC telesope (desribed in the previous Chapter) is a well-suited instrument to study the energy range between
Fermi
and Milagro. To selet possible
andidates for MAGIC, an interpolation of the uxes given by both experiments
was alulated in two dierent ways.
The Fermi Bright Soure List provides an
integral value above 1 GeV, whereas the Milagro soures are listed together with
their dierential ux points normalized at 35 TeV. Firstly, a power law interpolation
102
Chapter 7. MAGIC upper limits in the region of SNR G65.1
Figure 7.1:
Radio image of the region around SNR G65.1+0.6.
The numbered
objets are: (1) 3EG J1958+2909, (2) 2 CG 065+00, (3) 0FGL J1954+2838, (4)
0FGL J1958.1+2848, (5) region of dierent spetral index, (6) IRAS 19520+2759,
(7) bright ompat radio objet.
an be done from these two values, resulting in a ux value at 1 TeV and a spetral
index.
Sine the
Fermi
ux is likely to ontain both pulsar and steady emission,
this value is probably an overestimation.
Thus, a seond ux estimation may be
done by extrapolating the Milagro value to 1 TeV, assuming a power law index of
2.1. The expeted ux range optimal for MAGIC observations lies in between these
estimated values. Looking for interesting soures, those that were already observed
by MAGIC were ruled out (i.e. those in the H.E.S.S. san of the galati plane),
together with the ones that were below the threshold sensitivity. An interesting objet that did not fulll these harateristis appears in the region of SNR G56.1+06.
It turned out to be the pulsar 0FGL J1954.4+2838, with a alulated ux range of
2% − 4.9%
of Crab.
In fat, this region is densely populated, as an be seen in Figure 7.1, and
the objets it ontains and their likely assoiations is still a matter of debate.
G65.1+0.6 (dash-dotted shape) is a faint supernova remnant (SNR) rst reported by
et al. 1990℄. In [Tian & Leahy 2006℄, a distane of 9.2 kp and a Sedov
age of 40 − 140 kyr were suggested. Despite its distane, it is a very extended objet
′
′
(90 × 50 ). Very lose to the already mentioned Fermi soure (labeled 3 in the
[Landeker
Figure 7.1), there is a strong ompat radio objet (7). In the southern rim of the
shell, a region with dierent spetral indexes (5), originally thought to be an extra-
7.2. Observations
103
galati objet [Seiradakis
et al.
1985℄, an be found. Also, the nearby pulsar PSR
1957+2831 (X) may be assoiated to the remnant [Tian & Leahy 2006℄, due to the
ompatibility of its harateristi age. Looking at longer wavelenghts, the infrared
soure IRAS 19520+2759 (6) has been suggested to be at a similar distane of the
SNR and, given that it has assoiated a CO line, a H2 O and OH maser emission,
an interation between the moleular loud and the remnant ould be a possible
senario [Arquilla & Kwok 1987℄.
The gamma-ray emission in the region of G65.1+0.6 was rst deteted by the
COS-B satellite [Swanenburg
et al.
1981℄ as 2CG065+00, and later onrmed by
the EGRET satellite (3EG J1958+2909) in [Hartman
extension or multiple soures were denoted.
et al.
1999℄, where a possible
ould larify their signal as aused by the two soures 0FGL
0FGL J1958.1
+ 2848
Fermi
J1954 + 2838 and
But it was only reently that
(3 and 4 in Figure 7.1).
Observing the SNR G65.1+06 region, MAGIC was expeted to deliver the following sienti results:
•
Establishing the loation of the
one of
Fermi.
γ−ray
soure with a resolution exeeding the
This might larify whether the origin of the radiation omes
from inside the shell, or even from a ompat objet.
•
Obtaining a omplete spetrum, together with
haraterize the soure at very high energies.
Fermi
and Milagro results, to
On the one hand, the result
may shed some light to onrm the SNR as the soure of the emission. On
the other hand, if no signal is found, it would imply that the Milagro objet
is not idential to the
Fermi
Bright soure.
For instane, Milagro ould be
seeing the interation between the SNR and the moleular loud. In this ase,
one of the pulsars (1957+2831 or 1954+2838) may not belong to G65.1+0.6.
•
Proting from the inlusion of other objets in the eld of view of the amera
to obtain hints to other detetions. These other objets are a pulsar, the rim
of the SNR and the infrared region, among others.
The results of the study of this region were published in the Astrophysial Journal in 2010 [Aleksi¢
et al.
2010℄, and the PhD student is one of the orresponding
o-authors in this paper.
7.2 Observations
The observations were entered on the Fermi Bright soure 0FGL J1954.4
+ 2838
(from now on referred as J19540 ) in July and August 2009. The observations were
arried out in wobble mode (see previous Chapter, or [Fomin
yielded two datasets with osets of
±0.4◦
et al.
1994℄), whih
in RA from this soure, see Figure 7.2.
The wobble position was alterned every 20 min, and the data were taken at zenith
angles between 0 and 40 degrees.
At the time, the MAGIC-II telesope was still
104
Chapter 7. MAGIC upper limits in the region of SNR G65.1
under omissioning, therefore the analysis performed here uses only the data from
the stand-alone MAGIC-I telesope.
Summer observation time at the MAGIC site usually implies alima: dust suspended in the atmosphere oming from the Sahara desert, that interferes with the
quality of the data taking. Therefore, from the total amount of time observed, only
24.7 hours survived the quality seletion uts. Those uts were applied to the data
runs mainly based on the steadiness of the event rate after image leaning, but also
onsidering a few parameters that haraterize the transpareny of the atmosphere,
suh as the sky temperature and humidity. An additional ut removed the events
with a total harge (size ) of less than 100 photoeletrons, thus providing a better
bakground rejetion.
As it was previously stated, this region inluded other interesting objets. Speifially, there was another
Fermi
soure, 0FGL
J1958.1 + 2848
(shortly referred as
J19580 ), in the eld of view of one of the two wobble positions. 12.6 hours of eetive
observation time were analyzed for this objet.
7.3 Data analysis
Eah data set was analyzed in the MARS analysis framework (see previous Chapter,
[Moralejo
et al.
2009℄), standard software for the analysis of MAGIC data. To look
for the signal oming from the two Milagro-deteted
analysis was performed, using
θ2
that when the 1-year atalog of
plots and skymaps.
Fermi
soures [Abdo
Fermi
soures, a standard
It shall be noted, though,
et al.
2010a℄ was released,
the exat oordinates of both now identied pulsars (1FGL J1954.3
1FGL J1958.6
+ 2845,
+ 2848,
and
in short J1954 and J958, respetively) hanged respet to
the ones given in the previous Fermi Bright Soure list (0FGL J1954
0FGL J1958.1
+ 2836
+ 2838
named in this text J19540 and J9580 , respetively).
and
The
whole analysis had to be repeated, this time using the latest more aurate soure
positions.
Both soures had to be analized dierently.
In the ase of J1954, a standard
wobble analysis ould be done: in suh ase, the exposure inhomogeneities anel
out when omparing the photon ux from the soure to the one on the opposite
side of the amera (alled anti-soure, see Figure 7.2). However, for J1958, a wobble
analysis using only one of the two wobble positions does not guarantee this anelation. Therefore, the analysis was done in ON/OFF mode, using the near wobble
sample as ON-soure data and the far wobble sample as OFF-soure data. Having
the OFF-soure at the same position in relative amera oordinates as the soure in
the ON sample, the exposure inhomogeneities may anel out.
Figure 7.3 shows the
θ2
distributions for eah soure, where the values in the
horizontal axis represent the squared angular distanes between photon diretions
and the soure position. In the ase of having a very high energy (VHE) gamma-ray
emission oming from the observed soure, an exess is expeted to appear for low
θ2
values, see setion 6.3.1.
This exess omes from substrating the bakground
7.3. Data analysis
105
30.0
Fermi J1954
Fermi J1958 (only in W1)
1420 MHz G65.1+0.6 shell
Milagro 3 contour
MAGIC Pointing Positions
MAGIC Off J1954
MAGIC Off J1958 (only in W2)
DEC (2000)
29.5
29.0
W1
28.5
W2
28.0
20.00
19.95 19.90
RA (2000)
Figure 7.2: Observation setup for the two
Fermi
19.85
soures J1954 and J1958 in the
ontext of SNR G65.1+0.6 and a Milagro signiane ontour. J1958 appears only
in one wobble position (W1), so the OFF data is taken from the other wobble
sample, using the same position relative to the pointing diretion. The outline of
the remnant is taken from the radio map in [Landeker
of the Milagro signiane ontour [Abdo
spread funtion.
et al.
et al.
1990℄. The extension
2009i℄ is ompatible with their point
106
Chapter 7. MAGIC upper limits in the region of SNR G65.1
1FGL J1958.6+2845
Entries 80393
Entries 39006
# Events
# Events
1FGL J1954.3+2836
300
700
250
600
500
200
400
150
300
100
200
50
100
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Figure 7.3: Plots showing the
0.45
θ2
0
0
0.5
θ2
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
θ2
distributions for J1954 (left) and J1958 (right).
The shapes of the ON and OFF distributions agree well with eah other in both
soures, whih means there is no
γ−ray
signal. The dashed lines indiate the signal
regions.
to the number of events around the soure position (ON events), having previously
estimated the bakground by ounting the events around the anti-soure position
(OFF events). The number of OFF regions explored in the analysis of J1954 was one
and three, although only the last option is shown in the Figure 7.3. Therefore, the
unlikely ase of an emission ouring by hane at both ON and OFF loations at
a similar ux level is disarded. Furthermore, a ut in
hadronnes
of 0.1 was applied
to improve the bakground estimation and determine the signal region separately
in both soures. No signiant signal ould be found in any of the soures.
In order to nd a signal using a blind searh (i.e., regardless of the soure position), skymaps in a region of
same uts in
hadronnes
2.8◦ × 2.0◦
were drawn in dierent energy ranges. The
(0.1) and size (100) as in the
θ2
plots were applied to the
maps. Figure 7.4 shows the skymap for both soures above 200 GeV. No signiant
signal ould be found in any of the skyplots in either of the soures.
7.4 Upper limits on the gamma-ray ux
Sine no signal ould be retrieved from the SNR G65.1+0.6 region, upper limits were
alulated of the integral and dierential ux. To obtain the dierential upper limit
(u.l.) values, the data was divided into three bins of estimated energy (starting from
120 GeV, going to 375 GeV, then 2.8 TeV and nally 12 TeV). From the
θ 2 -plots,
an
95% ondene level (.l.) for eah bin,
et al. 2005℄. An eieny systemati error
event number upper limit was alulated at
using the method desribed in [Rolke
of
30%
was assumed [Albert
et al.
2008b℄.
To alulate the ux upper limit, the
number of events per energy bin is established to be:
N = tef f
Z
Φ(E)Aef f (E)dE
(7.1)
7.4. Upper limits on the gamma-ray ux
107
Figure 7.4: Skymaps of the exess events (top) and signiane (bottom) for J1954
(left) and J1958 (right). The blak star shows the enter of the pointed soure, the
white irle represents the MAGIC point spread funtion (PSF) at mid energies.
The distribution of signianes are well-tted with a simple gaussian.
108
Chapter 7. MAGIC upper limits in the region of SNR G65.1
Table 7.1:
Dierential upper limits for both soures, for the present rosshek
analysis.
Soure Name
1FGL J1954.3+2836
Extension
(deg)
≤ 0.08
1FGL J1958.6+2845
≤ 0.08
where
Φ
F95%
(10−12 TeV−1 m−2 s−1 )
25
0.5
0.022
76
0.71
0.033
is the ux (photons per unit of time, energy and area),
tive time of observation and
Aef f (E),
Signiane
(σ )
-1.4
-1.0
+2.2
-1.0
-0.9
+0.7
Emed
(GeV)
221
980
5686
221
966
5123
Aef f
tef f
is the ee-
is the eetive area after uts. To simulate this
a power law energy spetrum with a photon index of
−2.1
is assumed for
eah energy bin:
Φ=K
E
E0
−2.1
(7.2)
where K is a normalization fator. The inuene of the photon index is minor, sine
the energy ranges are suiently small. One the upper limit is derived from the
number of events (Nul ), the onversion to ux upper limits uses (in eah energy
bin):
K≤
The mean
γ−ray
Nul
R
tef f (E/E0 )−2.1 Aef f (E)dE
(7.3)
energy in eah bin of reonstruted energies, after all uts, an be
obtained through Monte Carlo simulations, sine the data an only be seleted by
an estimated energy.
Until this point, the analysis was performed assuming the soures were pointlike, i.e.
the extension was supposed similar or smaller than the PSF of MAGIC
(dened as the sigma of a two dimensional Gaussian funtion). For this ase, it was
◦
onsidered to be 0.08 . In this partiular region, though,
γ−rays
may ome from
an extended soure (a PWN or the shell of the SNR). Therefore, another upper
◦
limit for the ux was alulated, assuming an extension of 0.3 .
This partiular
value was hosen beause the biggest TeV PWNe have sizes of few tens of parses,
whih at the distane of G65.1+0.6 would be within this radius.
Inreasing the
signal integration radius, more bakground events are inluded and that leads, thus,
to higher upper limits. The derived
95%
.l. ux upper limits are summarized in
Table 7.1. The dierenes between the limits of J1954 and J1958 are all ompatible
within the statistial utuations.
Also, an integral upper limit above 200 GeV was derived for eah soure. The
results were
3 × 10−13
−1 m−2 s−1 for J1954 and
TeV
4 × 10−13
−1 m−2 s−1 for
TeV
J1958, whih an also be translated in ommonly used units as 3% and 2% of Crab
Nebula ux, respetively.
7.5. Interpretation and disussion
109
Table 7.2: Charateristi parameters of the two Fermi pulsars 1FGL
and 1FGL
J1958.6 + 2845,
J1954.3 + 2836
refereed as J1954 and J1958, respetively. See referenes
in the text.
Parameters
1FGL J1954.3+2836
1FGL J1958.6+2845
69.5
21
Age (kyr)
Period (ms)
Spin-down luminosity (erg/s)
290
92.7
10.48 × 1035
3.39 × 1035
2.9
1.2
Energy ut-o (GeV)
7.5 Interpretation and disussion
When the 1-year
Fermi
Catalog was released,
γ−ray pulsars thanks to a blind
et al. 2009d℄ and [Abdo et al. 2010b℄).
ported as
[Abdo
J1954 and J958 ould be re-
searh ([Saz Parkinson
et al.
They appeared to be normal
2010℄,
Fermi
pulsars, as an be seen in their harateristi parameters listed in the table 7.2.
Before this happened, signianes of
4.3 σ for J19540 and 4.0 σ for J19580
et al. 2009i℄. Given that the angular
laimed as detetions by Milagro [Abdo
lution of Milagro is about
0.4◦ − 1.0◦ ,
were
reso-
those values are still orret for the 1-year
atalog positions of the soures, whih are oset by
≤ 0.1◦ .
Flux values were de-
termined for a harateristi median energy of 35 TeV. As it is shown in Figure 7.1,
the region of SNR G65.1+0.6 is densely populated, and Milagro soures ould be
assoiated with the
Fermi
pulsars, a possible extragalati soure, a moleular loud
interating with the SNR or a radio ompat objet (see setion 7.1 for further details). However, the most likely assumption was that they were indeed related to the
objets observed by
Fermi,
i.e., that they were PWNe or, in the ase of J1954, the
shell of the SNR, whih surrounds the pulsar. Gamma-rays at TeV energies ould
also be produed in an interation of the shell with a oinident moleular loud,
suh as the infrared soure IRAS 19520+2759 (gure 7.1).
The upper limits alulated on the ux at 1 TeV, at the maximum of the MAGIC
sensitivity, present values of 3% and 2% of Crab for J1954 and J1958, respetively.
Therefore, the photon index in the energy range of 1 to 35 TeV must be harder than
2.2 for J1954, and 2.1 for J1958, if an assoiation between the Milagro and the
Fermi
objets is assumed and they are treated as point-like objets. The spetral energy
distribution (SED) would be thus likely to peak at energies greater than 1 TeV. On
◦ is assumed, the orresponding ux limits
the other hand, if an extension up to 0.3
in Crab Nebula units are
14%
for J1954 and
3%
for J1958. In this extended ase,
the photon indies would be limited to values inferior to 2.6 and 2.2, respetively.
A omplete SED, overing from the
Fermi
to the Milagro energies, an be on-
struted by adding the MAGIC upper limits (see Figure 7.5).
From this general
piture, it an be stated that the most likely senario to explain the gamma ray
emission deteted by Milagro might be the presene of two PWNe, assoiated with
the
Fermi
pulsars. Given the old ages of the pulsars (see table 7.2), it is reasonable
Chapter 7. MAGIC upper limits in the region of SNR G65.1
10-10
10-10
10-11
·
·
10-11
MAGIC (95% U.L.)
MAGIC < 0.3 deg (95% U.L.)
Milagro
Fermi PSR Cat. Fit
Fermi 1-Year Catalog
Egret
3% Crab (MAGIC)
Flux E2 (TeV cm 2 s 1 )
MAGIC (95% U.L.)
MAGIC < 0.3 deg (95% U.L.)
Milagro
Eight blind PSR Fit
Fermi 1-Year Catalog
3% Crab (MAGIC)
Flux E2 (TeV cm 2 s 1 )
110
10-12
10-1 100 101 102 103 104 105
E (GeV)
10-12
10-1 100 101 102 103 104 105
E (GeV)
Figure 7.5: Compilation of ux measurements and upper limits for: (left) 1FGL
et al. 2010, Abdo et al. 2010a℄ , (right)
1FGL J1958.6+2845 from EGRET [Hartman et al. 1999℄, Fermi [Abdo et al. 2010b,
Abdo et al. 2010a℄, together with MAGIC and Milagro [Abdo et al. 2009i℄ data.
The 3% fration of the MAGIC Crab spetrum [Albert et al. 2008b℄ is shown for
J1954.3+2836 from
Fermi
[Saz Parkinson
omparison.
to expet an inverse ompton omponent that dominates their energy outows, and
onsequently the VHE emission to be extended [de Jager & Djannati-Ataï 2009℄,
[Tanaka & Takahara 2009℄.
7.6 Conlusions
After the analysis of nearly 25 hours of good quality data in the region of the
SNR G65.1+0.6, no signiant
γ -ray emission ould be found in the MAGIC energy
range (from hundreds of GeV to several TeV). In that same region, the Milagro
ollaboration had reported the emission of
and the
J1958.6
γ -rays,
with a median energy of 35 TeV,
Fermi satellite had deteted two pulsars, 1FGL J1954.3 + 2836 and 1FGL
+ 2845. The lak of detetion with the MAGIC-I telesope, both using the
a-priori soure-position analysis and a skymap of the area, yielded three dierential
ux upper limits for eah soure.
In the light of MAGIC results, the ux upper limits support the senario in whih
the multi-TeV emission measured by Milagro is aused by a dierent mehanism than
the emission deteted by
Fermi.
Taking into aount the ages of the pulsars and the
SNR, the existene of two old PWNe powered by the two GeV pulsars is one of
the likely senarios.
Chapter 8
Simulations of CTA response to
partiular siene ases
Contents
8.1 Sorting out dierent layouts and ongurations for CTA . 111
8.2 A brief look at starting-up tools . . . . . . . . . . . . . . . . 113
8.3 Spetral studies . . . . . . . . . . . . . . . . . . . . . . . . . . 115
8.3.1
Moleular louds illuminated by CR from nearby SNR . . . .
116
8.3.2
Starburst galaxies M82 & NGC 253 . . . . . . . . . . . . . .
118
8.4 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
The CTA experiment (Cherenkov Telesope Array)
1 has been dened as the
next generation of telesopes using the Cherenkov tehnique. In the energy range of
few TeVs, the CTA sensitivity will improve by one order of magnitude ompared to
the previous generation experiments (like MAGIC or H.E.S.S.). In addition, the energy range will also be expanded, from 0.01 to 100 TeV, thanks to the large number
of dierent sized Cherenkov telesopes. Furthermore, an improvement regarding the
angular resolution is expeted by ahieving a better resolution and higher photon
statistis that an rene the imaging of the air showers. In order to ahieve full-sky
overage, two arrays will be built:
one in the northern and one in the southern
hemisphere. The northern site is planned to fous on extragalati soures, whereas
the southern one will take are of the galati soures, speially sine it will over
the entral galati plane. CTA is planned as an open observatory, with transparent
aess to data, analysis tools and user training.
perfomed [Hofmann
et al.
The main design work has been
2010℄, and now it is faing the prototyping and onstru-
tion phases. Simulations of CTA response to interesting siene ases are presented
below.
8.1 Sorting out dierent layouts and ongurations for
CTA
At an early stage of the design of the CTA array, several layouts were generated, eah
of them with dierent distributions and types of telesopes. These ongurations
1
http://www.ta-observatory.org/
112 Chapter 8. Simulations of CTA response to partiular siene ases
Figure 8.1: Konrad Bernlöhrs adapted layout of the original ultra-CTA (from Padova
2008 CTA meeting). Four types of telesopes are plotted, see table 8.1 for details,
being 1 = red, 2 = green, 3 = blue and 4 = magenta.
Table 8.1: Main harateristis of dierent types of telesopes for CTA.
Area
Diameter
F.o.V.
Pixels
2
23 m
5
◦
0.09
◦
2
11 m
8
◦
0.18
◦
7m
◦
10
0.25
◦
11 m
10
◦
0.18
◦
1
412 m
2
100 m
3
2
37 m
4
100 m
2
8.2. A brief look at starting-up tools
113
Figure 8.2: Layout ongurations of the three representatives: B (left), D (enter), I
(right). The types of telesopes orresponds to the ones detailed in Table 8.1, being
1 (red), 2 (green), 3 (blue), 4 (magenta), the number in brakets orresponds to the
eld of view of eah telesope.
of CTA were originally taken as subsets of the so-alled ultra-CTA (see Figure 8.1),
and were seleted ensuring a similar onstrution ost. The initial studies for the
Physis group started with these 11 ongurations (named from A to K). The very
rst step onsisted on grouping and omparing all of them in order to understand
their intrinsi harateristis and make any subsequent analysis easier.
The nal
goal was to work only with one representative onguration from eah group, and
analyze dierent soures with these representatives.
All the ongurations were lassied, in a rst approximation, by looking at
the dierential sensitivity, and maximizing their response at low energies (LE),
high energies (HE) and over the whole energy range. In the end, three simulated
ongurations were hosen from eah group with the following harateristis:
•
Compat distribution with bigger telesopes, optimized at LE.
•
Extended distribution with mid-size telesopes, optimized at HE.
•
Mix of the previous two: optimized over the whole energy range.
The hoies were validated omparing eah representative to the rest of the
ongurations of their respetive groups. Then, deviations from the representative
were alulated, quantifying the goodness of the representative with respet to the
others in the same group.
Finally, omparing the angular and energy resolution, the hosen ongurations
were still good representatives at LE, HE and over the whole energy range, see
Figures 8.4 and 8.5. One the ongurations were suessfully lassied, the three
representatives (B, D, I) were used to simulate the spetra and light urves of spei
soures, whih ould be interesting ases for CTA.
8.2 A brief look at starting-up tools
In the following setions, the simulated response of CTA has been alulated using
the following maros provided by Daniel Mazin:
114 Chapter 8. Simulations of CTA response to partiular siene ases
Figure 8.3:
Dierential sensitivity of the three representative ongurations:
D
(red), B (blue), I (green), in Crab units (C.U.) for 50 hours of observation.
Figure 8.4: Angular resolution (80% ontainment radius) of the three representative
ongurations, see Figure 8.3, for best resolution (left) and best sensitivity (right).
8.3. Spetral studies
115
Figure 8.5: Energy resolution of the three representative ongurations, see Figure
8.3, for best resolution (left) and best sensitivity (right).
• makeCTAspe.C :
• testCTA.C :
Simulates CTA spetral points for a given soure,
Calls previous maro and draws the spetrum.
Moreover, the simulations depend on the layout ongurations. Their performane
les ontain information on the eetive area, the dierential sensitivity, the bakground rate and the angular resolution (68% and 80% ontainment).
The main ingredients for the program
makeCTAspe.C
are the intrinsi spetral
shape and ux of the hosen soure, the aorementioned eetive area and the
observational time.
In the ase of soures outside our Galaxy, the extragalati
bakground light (EBL) attenuation an be taken into aount. The seletion riteria
for data points require more than 3 sigma, a number of exess events greater than
10 and the exess 1% above the bakground signal. If the number of exess events or
signiane is too low, the spetrum is re-binned. Additionally, the ON events are
alulated randomly aording to the Poisson statistis with a given mean value.
In the ase of an extended soure, the bakground ux is integrated.
When the
simulation is ompleted, the maro provide the dierential energy spetrum and the
integral ux in a spei energy range. On the other hand,
testCTA.C
handles the
user interfae, by introduing the atual onguration le of the CTA performane,
the funtion of the soure spetrum, the observation time and the size of the soure
extension.
Also, attenuation an be applied if needed, as well as redening the
energy range.
The use of these tools, thus, provide CTA simulated data points for the spetral
energy distribution of dierent interesting soures, as shown in subsequent setions.
8.3 Spetral studies
Every simulated layout for CTA provides dierent advantages and disadvantages
when observing dierent objets in the sky. Atually testing the behaviour of in-
116 Chapter 8. Simulations of CTA response to partiular siene ases
Figure 8.6: Total gamma ray emission from a moleular loud of mass
ated at a distane of 1 kp.
105 M⊙
lo-
The distane between the moleular loud and the
SNR is 50, 100 and 200 p for left, enter and right panel, respetively. The solid,
dotted, and dashed lines refer to the emission at 2000, 8000 and 32000 years after
the SN explosion. Private ommuniation from S. Gabii, based on gure 5 from
[Gabii
et al.
2009℄.
teresting gamma-ray soures with CTA simulations will help to hoose whih one
of those ongurations is favoured. In the next setions, initial spetral studies on
dierent objets are shown in order to obtain estimations for unexplored energy
ranges, new spetral features and model validations. These objets are in a ertain
way related to osmi ray diusion, either in our galaxy (IC 443, moleular louds
lose to supernova remnants) or in others (starburst galaxies M82 and NGC 253).
The ase of IC 443 is detailed in the next Chapter.
8.3.1 Moleular louds illuminated by CR from nearby SNR
Non-thermal emission is expeted to ome from moleular louds, due to interations of osmi rays (CR) penetrating the loud.
This emission would be en-
haned if the moleular loud is in the proximity of a supernova remnant (SNR)
[Gabii
et al.
2009℄, [Rodríguez Marrero
et al.
2009℄.
The CR spetrum has two
ontributions:
•
Galati bakground: haraterized by a steep spetrum, steady in time, that
peaks in the GeV energy region;
•
Runaway CRs from SNR: present a hard spetrum, variable in time.
This
seond peak appears at TeV energies and moves to lower and lower energies:
the higher the energy, the earlier and faster CRs diuse away.
When superimposing both ontributions, a urious onave spetra appears. This
V-shape is reeted in gamma-rays, given that above 100 MeV, the spetrum is dominated by emission oming from neutral pion deay (π0
of
Fermi
→ γγ ).
If joint observations
and ground based Cherenkov telesopes were arried out, the detetion of
suh a shape ould prove the presene of a CR aelerator lose to moleular louds.
E2 dN/dE (TeV cm-2 s-1)
8.3. Spetral studies
117
intrinsic spectrum at 50 pc
intrinsic spectrum at 100 pc
intrinsic spectrum at 200 pc
expected spectrum (CTA) at 50 pc
expected spectrum (CTA) at 100 pc
expected spectrum (CTA) at 200 pc
-9
10
-10
10
-11
10
-12
10
-13
10
-14
10
0.01 0.02
0.1
0.2
1
2 3 45
10
Figure 8.7: Gamma-ray emission from a moleular loud of
20 30
100
energy E(TeV)
105 M⊙
illuminated by
an aelerator (whih explosion ourred 2000 yrs ago) and simulated with layout
onguration I, for 20 hours of observation.
The moleular loud is loated at
a distane of 1 kp from the observer and plaed at dierent distanes from the
aelerator: 50 (blak), 100 (blue), 200 (red) p.
One of the theoretial studies on this topi, by [Gabii
et al.
2009℄, was used
in the present work to simulate a response with CTA. In Figure 8.6, the gamma
emission oming from a moleular loud near a SNR is plotted.
The moleular
5
loud, loated at 1 kp from the observer, has a mass of 10 M⊙ . Considering that
the main bulk of gamma-ray emission omes from
π0
deay, the urves show the ux
at dierent epohs after the supernova (SN) explosion and at dierent separations
from the aelerator. The larger this separation is between the moleular loud and
the SNR, the lower is the level of CR ux that omes from the aelerator, as seen
in the panels from left to right.
There is also an evolution in time, proportional
to the square of the separation. In eah panel, the peak moves to lower and lower
energies with time (from right to left) due to the fat that CR with lower and lower
energies an progressively reah the loud.
Considering a xed time sine the SN exploded (2000 years, solid urve in Figure
8.6), dierent separations between the SNR and the loud are simulated in Figure
8.7. Observing 20 hrs, peuliar features in the spetra an already be seen at the
CTA sensitivity. A broad distribution with big telesopes at the enter (I) appears
as the best hoie to over low and high energies. An additional omponent should
arise at lower energies (Fermi range) due to the ontribution of CR from galati
bakground.
118 Chapter 8. Simulations of CTA response to partiular siene ases
CTA will be able to distinguish moleular louds illuminated by esaping osmi
rays from a nearby SNR. The expeted softening at lower energies, however, is hardly
reahable, leaving the whole V-shape spetrum to be obtained by a ombination of
Fermi
and CTA data.
In order to get enough statistis, from 20 to 30 hours of
observation time are needed. Moreover, the onguration I seems more suitable to
allow a better understanding of every possible feature in the spetra.
Promising as these results appear, there are however some aveats inherent to
the model.
Despite the large mass of the simulated loud, these type of objets
tend to be even more massive and extended. Therefore treating the soure as pointlike may be a bit optimisti.
Also, the largest separation of the loud and the
SNR, 200 p, is translated in angular distane in the sky as
is larger than the average detetors' eld of view.
target and aelerator beomes more diult.
∼ 6
degrees, whih
Thus, the assoiation between
Finally, the distane at whih the
moleular loud is loated probably will need to be readjusted, given that there are
not so many andidates at 1 kp. W28, an already deteted gamma-ray soure, is
onsidered a possible assoiation of a moleular loud and a SNR and it is loated
at 1.5 kp.
8.3.2 Starburst galaxies M82 & NGC 253
Starburst galaxies are haraterized by an enhaned star formation and supernova
(SN) explosion rate.
Sine SNe are believed to aelerate osmi rays, whenever
they are found in dense environments, like the entral regions of starburst galaxies,
gamma-ray emission has been predited to appear as a result of proton-proton interation and subsequent neutral pion deay. Reently, two of their most representative
members, M82 and NGC 253, have been deteted at GeV -TeV energies. In the lower
Fermi satellite was responsible of the detetion of both galaxies above
et al. 2010℄. At higher energies, both Cherenkov array experiments
VERITAS and H.E.S.S. deteted M82 above 700 GeV [Aiari et al. 2009a℄ and NGC
253 above 220 GeV [Aero et al. 2009℄, respetively. See table 8.2 for details on those
energies, the
100 MeV [Abdo
detetions.
The very long observational time required to detet these two starburst galaxies
by ground based gamma-ray experiments (more than a hundred hours), disesteemed
further studies on these interesting objets. However, sine these two galaxies are the
losest ones to us (therefore, easier to resolve), a deeper knowledge will shade some
light on CR diusion and gamma-ray absorption, among other spetral peularities.
Hopefully, CTA will help in these aspets and may also open the door for future
population studies on these and other related objets, like globular lusters.
As a rst approah to the problem, a simulation of the spetra of both galaxies
was performed using H.E.S.S. and VERITAS data. The model explained in Chapter
5, see also [Domingo-Santamaría & Torres 2005℄, [de Cea del Pozo
et al.
2009b℄, has
been taken as input. In Figure 8.8, the urves that arise from the modeling of both
spetra are shown, together with the data points obtained by the dierent gammaray telesopes. For M82 (left), the spae parameter studied (green shaded region
8.3. Spetral studies
119
Table 8.2: Summary of the observational detetions of M82 and NGC 253 by
Fermi
(at high energies, HE), VERITAS and H.E.S.S. (very high energies, VHE). The
energy thresholds for the integral ux alulations are: above 100 MeV in the ase
of
Fermi
LAT observations, above 700 GeV for VERITAS, and above 220 GeV for
H.E.S.S.
HE
VHE
Signiane (σ )
Time observed
Integral ux
(10−8 m−2 s−1 )
Dierential photon index
Signiane (σ )
Time observed
Integral ux
(10−13 m−2 s−1 )
Dierential photon index
M 82
6.8 (Fermi )
1 year
1.6 ± 5stat ± 0.3sys
NGC 253
4.8 (Fermi )
1 year
0.6 ± 0.4stat ± 0.4sys
2.2 ± 0.2stat ± 0.05sys
4.8 (VERITAS)
137 hrs
3.7 ± 0.8stat ± 0.7sys
1.95 ± 0.4stat ± 0.05sys
5.2 (H.E.S.S.)
119 hrs
5.5 ± 1.0stat ± 2.8sys
2.5 ± 0.6stat ± 0.2sys
-
Figure 8.8: Spetral modeling of the gamma-ray emission of the two losest starburst galaxies M82 (left) and NGC 253 (right).
The overlaid blue box orre-
sponds to the range of energies that CTA is predited to observe (from a few
tens of GeV to
by
Fermi
∼
100 TeV). Data points in both plots orrespond to detetions
(diamond), VERITAS (star) and H.E.S.S. (square). Figures taken from
[de Cea del Pozo
et al.
2009a℄. For a omplete explanation, see Chapter 5.
120 Chapter 8. Simulations of CTA response to partiular siene ases
from [de Cea del Pozo
et al.
2009b℄) satisfatorily explains the deteted high and
very high energy emission oming from the galaxy.
One of the possible urves in
that region, stating a rate of 0.2 supernova explosions per year (solid blak), is used
as input for the simulation. In the ase of NGC 253 (right), given the unertainty
in the distane to the galaxy (from 2.5 up to 3.9 Mp), a set of urves an aount
for the ux at these high energies [de Cea del Pozo
et al.
2009a℄. The urve seleted
for the simulation orresponds to a distane of 3.9 Mp (solid red), given that it has
the highest ux normalization at the CTA energy range.
Simulating 30 hours of observation with CTA, the spetrum of the starburst
galaxy M82 is learly seen in Figure 8.9. Three dierent array ongurations were
tested: the three representatives extrated in setion 8.1. The ompat onguration
(B) gives slightly better overage at lower energies (0.1 TeV), whereas the more
extended ongurations (D or I) over niely the last part of the spetrum (up to
10 TeV). In eah ase, a muh better reonstruted spetrum is ahieved, ompared
to the existing data points from
Fermi
and VERITAS (in grey).
However, when studying the ase of NGC 253, 30 hours were not enough to
obtain a ondent detetion of the galaxy. Indeed, at least 50 hours of observation
appear to be the estimated time to guarantee a detetion and reonstrution of
the spetrum of this soure, as seen in Figure 8.10. Again, the three representatives
were tested (but only one is shown), and the best results are obtained when using an
extended array onguration (either I or D). Although surprising as it may seem that
the H.E.S.S. integral data point is below the CTA sensitivity, it should be reminded
that a speial analysis tehnique alled model analysis
2 was used to obtain suh
detetion.
The results for NGC 253 were not as promising as for M82, regarding a statisially well reonstruted spetrum in a reasonable time (around 30 hours). Nonetheless, it seems that CTA will be able to detet starburst galaxies. For a better understanding of all possible spetral features, onguration D or I seem more suitable,
i.e., extended array ongurations with or without bigger telesopes at the enter
that provide a good reonstrution of low energy gamma showers.
Future works
on this topi ould be determining how far away CTA an detet other starburst
galaxies, so that a population study an be performed.
8.4 Future work
The CTA observatory will open a wider range of energies (from tens of GeV to tens
of TeV) to study gamma-ray astronomy, providing better sensitivity and angular resolution. A thorough study is intended to be arried out, among other topis, on the
2
The Model Analysis is based on a omparison and t of observed air shower images with a
preomputed library of images [de Naurois & Rolland 2009℄. It was trained with simulated gamma
rays and with real osmi-ray data from bakground elds [Ohm et al. 2009℄. The algorithm yields
an improvement by a fator 1.5 to 1.7 in the statistial signiane of faint soures ompared with
the standard image analysis [Aharonian et al. 2006a℄, [Aero et al. 2009℄, as veried with a number
of other gamma-ray soures.
8.4. Future work
121
Figure 8.9: M82 spetrum as simulated for CTA for 30 hrs with onguration B
(top), D (enter), I (bottom). The grey points orrespond to observational data: at
lower energies, an upper limit (68% .l.)
from
Fermi,
and at higher energies, the
dierential data points and an upper limit (99% .l.) from VERITAS.
122 Chapter 8. Simulations of CTA response to partiular siene ases
Figure 8.10: NGC 253 spetrum as simulated for CTA in 50 (left) and 70 hours
(right) with onguration D. The observational data (grey) orresponds to an upper limit (68% .l.)
from
Fermi ;
and H.E.S.S. integral data point (onverted to
dierential ux)
origin of Galati CR, their propagation within galaxies, and their interation with
the environment. For a long time, supernova remnants (SNR) have been thought
to be the soures of CR. To test this hypothesis with CTA, population studies are
needed in order to inrease the number of deteted SNR and improve statistis on
these objets. In addition to this issue, a disussion on soure onfussion (due to the
large number of soures to be deteted in the galati plane) should be addressed.
Another test on the SNRs as the origin of CRs ould be done by improving the
quality of the spatial orrelation studies between
γ -rays
γ -rays
and X-rays, and between
and gas distribution at SNRs. This last probe is yet to be arried out with
CTA.
If SNRs are indeed responsible for the origin of galati CRs, then the most extended explanation for their aeleration is via diusive shok aeleration (DSA).
To better understand this proess with CTA, some studies have been already performed on the uto region in SNR gamma ray spetra (from IC 443, see next
Chapter, and also RX J1713.7-3946 [Aharonian
very high energy photons (i.e.
et al.
2004a℄).
The detetion of
signiantly above 10 TeV) from any SNR would
help to disriminate between hadroni and leptoni models, sine the Klein-Nishina
eet would dramatially suppress the gamma ray ux due to inverse Compton in
this energy domain.
Another topi that would shed some light on this aspet is
spatially resolving the spetra of SNRs possible thanks to the improved angular
resolution.
To better understand CR propagation it will be useful to study moleular
louds that present gamma-ray emission oming both from the CR bakground
and nearby aelerators (i.e. SNRs). In the rst ase, the so-alled passive moleular louds ould be used to trae the spatial distribution of CRs in the Galaxy
[Gabii 2008, Aharonian 2001, Issa & Wolfendale 1981, Casanova
et al.
2010℄. The
ase of moleular louds assoiated with SNR has been presented in setion 8.3.1.
These studies are important beause the detetion of the gamma ray radiation om-
8.4. Future work
123
ing from these moleular louds might onstitute an indiret evidene for the aeleration of CRs at SNRs and, sine the harateristis of the radiation are expeted
to depend on the CR diusion oeient, these studies might be used to onstrain
its value in the viinity of CR aelerators.
Another interesting work related to
this issue would be studying the ase in whih the aelerator is plaed inside the
moleular loud.
Finally, regarding the studies on starburst galaxies, as previously mentioned, a
breakthrough would ome from the disovery of more soures of this type, given the
improvement in sensitivity.
In any ase, it will also be important to explore the
already deteted starburst galaxies, not only their spetra (as in setion 8.3.2) but
also their extension and morphology. Regarding further spetra features, any steepening at the highest energies ould explain extra omplexity in the radiative partile
distribution, as presently needed to explain observational data and, ultimately, put
limits on partile aeleration in these systems. Last, investigating ux variability
would give reliability to CR-related emission senarios in any extragalati soure.
Chapter 9
IC 443 in MAGIC stereo and
prospets with CTA
Contents
9.1 Proposal and observations with MAGIC stereo . . . . . . . 128
9.2 Analysis and results . . . . . . . . . . . . . . . . . . . . . . . . 129
9.3 IC443 as seen in CTA . . . . . . . . . . . . . . . . . . . . . . . 131
As already introdued in Chapters 3 and 4, IC 443 is a well known supernova
remnant (SNR) in gamma-ray astronomy. One of the most striking fats is that the
entroids of these detetions at high and very high energies do not oinide, as an
be seen in Figure 9.2. There is a lear displaement between the MAGIC/VERITAS
soure and the EGRET/Fermi one. The EGRET entral position is loated diretly
towards the enter of the radio shell of the SNR, where the
Fermi
soure 0FGL
J0617.4+2234 is also loated. Meanwhile, the MAGIC soure is (in Galati oordinates) south of it, lose but beyond the 95% ondene level (.l.) ontour of the
EGRET detetion (blak ontours in Figure 9.1). As noted in [Albert
et al.
2007b℄,
the MAGIC soure entroid is positionally oinident with a giant loud in front
of the SNR (see also
12 CO ontours in Figure 9.1). If the
Fermi
soure is taken
as referene, the entroid is displaed 0.05 degrees from EGRET, 0.15 degrees from
MAGIC, and 0.12 degrees from VERITAS entroids.
Not only is there a dierene in the position, but there also seems to be a break
in the spetrum between these two ranges of energies.
If an extrapolation of the
spetrum of the EGRET/Fermi soure is performed into the VHE regime, a higher
ux and harder spetrum than the one observed by MAGIC is obtained. In fat,
suh a hange appears to be reeted on the
Fermi
data.
For a spetral energy
distribution (SED) from 200 MeV up to 50 GeV, it seems better explained with,
for instane, a broken power law that rolls over at about 3 GeV, steepening at the
highest energies to math in slope the one that is found by MAGIC.
The region of the sky in whih IC443 an be found ontains a pulsar wind nebula
(PWN) CXOU J061705.3+222127 [Olbert
et al.
2001℄, [Bohino & Bykov 2001℄.
However, in all energy bands, the entroid of the orrespondingly deteted soures
is inonsistent with this PWN (and the putative pulsar). For instane, the entroid
of the PWN is 0.26 degrees from the
Fermi
LAT entroid. Given the above fators,
a possible way of explaining a relation between the MAGIC soure and the SNR is
Chapter 9. IC 443 in MAGIC stereo and prospets with CTA
140
120
3.2
100
80
3
-5
160
3.4
excess events / 10 sr
b [deg]
126
60
40
2.8
20
0
PSF
2.6
-20
189.5
189
188.5
l [deg]
Figure 9.1: Sky map of gamma-ray andidate events (bakground subtrated) in the
diretion of MAGIC J0616+225 for an energy threshold of about 150 GeV in galati
oordinates. Overlayed are
12 CO emission ontours (yan) showing the position of
their maxima oiniding with the MAGIC detetion, and ontours of 20 m VLA
radio data (green), X-ray ontours from Rosat (pu
from EGRET (blak).
12 rple) and gamma-ray ontours
The white star denotes the position of the pulsar CXOU
J061705.3+222127. The blak dot shows the position of the 1720 MHz OH maser.
The white irle shows the MAGIC I PSF of
σ = 0.1◦ .
From [Albert
et al.
2007b℄
127
Figure 9.2: Loations and extensions of the 4 gamma-ray soures. Centroid positions
are marked with dierent symbols: EGRET (blue triangle), MAGIC (red downside
triangle), VERITAS entroid (green star) and
Fermi
LAT (blak diamond).
The
respetive loalization errors are shown as rosses. Best-t spatial extensions of the
Fermi
(ross-hathed band) and VERITAS (striped green band) soures are drawn
as rings with radii of
ext
θ68
and widths of
±1 σ
error. The PWN loation is shown as a
magenta dot. Contours are the loations and shapes of the loal shoked moleular
louds taken from [Huang
et al.
1986℄. Figure taken from [Abdo
et al.
2010g℄
128
Chapter 9. IC 443 in MAGIC stereo and prospets with CTA
ahieved through the diusion of osmi rays (CR). MAGIC J0616+225 is onsistent with the interpretation of CR interating with the giant moleular loud lying
in front of the remnant, produing no ounterpart at lower energies. In the model
by [Torres
et al.
2008℄, the nearby EGRET/Fermi soure an be produed by the
same aelerator, and in this ase, a o-spatial MAGIC soure is not expeted. For
further details on the model, see Chapters 3 and 4.
In order to further bridge the energy gap between
Fermi
and MAGIC, a proposal
for observing IC443 with MAGIC stereo system was made. Details of the proposal
and subsequent analysis are explained in the following setions.
9.1 Proposal and observations with MAGIC stereo
As it has been previously stated,
MAGIC I observations yield to the dete-
tion of a new soure of gamma-rays,
J0616+225.
This soure is loated at
h m s
◦
(RA,DEC)=(06 16 43 ,+22 31'48), with a statistial positional error of 1.5', and
a systemati error of 1'.
A simple power law was tted to the measured spetral
points through:
dNγ
= (1.0 ± 0.2) × 10−11
dAdtdE
E
0.4 TeV
−3.1±0.3
cm−2 s−1 TeV−1
(9.1)
with quoted errors being statistial. The integral ux of MAGIC J0616+225 above
100 GeV is about 6.5% of the Crab Nebula.
MAGIC observations in stereo mode ould provide, together with
Fermi,
on-
tinuous overage of the soure from 100 MeV up. It should be noted, though, that
by the time the proposal was made, no
Fermi
results were released. The intended
aims, bak then, were as follows:
•
To analyze the position of the soure as a funtion of dierent low-to-high
energy uts.
Thus, heking whether the soure moves towards the enter
(outskirts) of the SNR with lower (higher) energy threshold.
•
To nd whether the spetrum of the MAGIC detetion beomes harder as the
energy threshold dereases.
•
To extrat morphologial information (i.e., the extension of the soure) and
investigate a possible dependeny on the energy threshold.
The whole proposal was driven by the already explained senario in whih CR
would esape from the SNR and interat with the moleular loud in front of it.
The moleular loud environment surrounding IC 443 and its possible onnetion
with the EGRET gamma-ray soure was studied by e.g., [Torres
is a large amount of moleular mass (∼
et al.
2003℄. There
104 M⊙ ) onsistent with the distane to
the SNR, orresponding to a veloity range of
−20
to 20 km/s.
The highest CO
intensity deteted is diretly superimposed on the entral position of the MAGIC
soure.
9.2. Analysis and results
129
Aording to that senario, the displaement between EGRET and MAGIC
soures would have a physial origin.
Suh displaement would ome from the
dierent properties of the proton spetrum at dierent loations, whih in turn is
produed by the diusion of CRs from the aelerator (IC 443) to the target. Spei
preditions for future observations an be made as a result of the model presented
by [Torres
et al.
2008℄. At high energies, a morphologial and spetral hange from
the position of the loud (i.e. the enter of MAGIC J0616+225) towards the enter
of IC 443 should be seen. At a morphologial level, when observing at lower and
lower energies, the radiation will be deteted loser to the position of the SNR shell.
At a spetral level: suient statistis should show that the lower the gamma-ray
energy, the harder the spetrum is.
Measurements by MAGIC stereo and
Fermi
ould lead to the empirial determination of the diusion oeient in the medium.
Originally, the observations were planned during winter 2009 - 2010, but due to
bad weather onditions, only a small fration of the granted time was spent on the
data taking between January and February 2010. A preliminar analysis of the data
is presented below.
9.2 Analysis and results
Stereosopi observations were arried out in wobble mode, at two positions
away from the enter.
0.4◦
The reason for this observational mode was that the sky
region around the soure has a relatively high and non-uniform level of bakground
light. Within a distane of
∼1.5◦
from the soure, there are two bright stars, one of
them is brighter than 8 mag, eta Gem with 3.28 mag, and the other (a bit further
away) is mu Gem, with 2.88 mag. By hoosing one of the two wobble o-positions
oiniding with the brigthest star (eta Gem), a similar sky brightness distribution
an be ahieved in both wobble positions.
Although the soure ould be observed at good low zenith angles from November
2009 onwards, the stereosopi mode in MAGIC was still under omissioning. The
start of the data taking was then postponed until Deember 2009. By that time,
observations of the Crab Nebula (standard andle in gamma-ray astronomy) would
have been perfomed and analysed, and a deeper knowledge about the new system
ould have been ahieved. However, due to bad weather, only 7 hours were observed
between January and February 2010.
The proposal was re-submitted in the next
yle (2010 - 2011) to obtain more observational time, but unfortunately no more
time was granted.
The observations were taken at zenith angles below
30◦ , to ahieve the neessary
low energy threshold this study requires. At La Palma, IC 443 ulminates at about
6◦
(Γ
zenith angle (ZA). Sine the already deteted spetrum was found to be steep
=
−3.1 ± 0.3),
the intended study an better benet from low energy threshold
(thus the low zenith angle) and greater senstivity (granted by the new stereosopi
system).
Given the small amount of time observed (5 hours after quality uts), the
130
Chapter 9. IC 443 in MAGIC stereo and prospets with CTA
Figure 9.3: Plot showing the
θ2
distribution for the MAGIC soure in the region of
IC 443. The shapes of the ON and OFF distributions agree well with eah other.
A hint of signal is already seen in barely 3 hours of observations.
originally planned study ould not be performed, and a quik analysis was arried out.
The data olleted was analyzed in the MARS analysis framework
([Moralejo
et al.
2009℄), standard software for the analysis
1 of MAGIC data. Due to
the novelty of the stereo system, the analysis tools used were still under development
by that time.
In order to look for gamma-rays oming from the pointed soure, standard uts
for stereo were applied in
hadronness
and
size
(0.2 and 100, respetively). In the
θ2
2
distribution from Figure 9.3, an exess at lower angles an barely be seen, implying
that a hint of signal (
2 σ)
an be deteted. However, it is not enough for a spetral
reonstrution, nor the detailed study in the spetrum and morphology (in bins of
energy). The gamma-ray hint of signal is positionally oinident with the previously
published MAGIC J0616+225 soure. A skymap above 200 GeV, with the same uts
as the
1
2
θ2
plot, an be seen in Figure 9.4.
An example of one analysis of MAGIC data an be found at [Aleksi¢
a denition an be found in setion 7.3
et al.
2010℄
9.3. IC443 as seen in CTA
131
Figure 9.4: Skymap (map of signianes) of the SNR IC 443 (left) and distribution
of signianes (right) of the same region. The blak ross marks the position of the
MAGIC soure J0616+225. The white irle shows the PSF of the MAGIC stereo
system.
Table 9.1: Power law (p.l.) index for MAGIC-like or VERITAS-like spetrum for
IC 443, when simulating CTA response for 50 hrs in onguration I.
MAGIC-like spetrum
VERITAS-like spetrum
Observed p. l. index
CTA simulated p. l. index
3.1 ± 0.3
2.99 ± 0.38
3.14 ± 0.04
2.98 ± 0.03
9.3 IC443 as seen in CTA
Having in mind similar goals as in the MAGIC stereo proposal (see setion 9.1),
a preliminar spetral study on IC 443 was performed for CTA. The response of
the instrument was simulated using the tools and the three representative layout
ongurations desribed in the previous Chapter 8.
The energy range that CTA
would over goes from a few GeVs to hundreds of TeVs.
Initially, the observed
spetra (by satellite and ground based telesopes) were used as the
intrinsi
one,
speially the ones from the MAGIC and VERITAS experiments and the seond
range was from 0.02 to 0.07 TeV for the
Fermi satellite. The dened energy
Fermi spetrum, and from 0.07 to 7 TeV
for the MAGIC and VERITAS spetra.
The CTA response was simulated using
part of the broken power-law provided by the
Fermi /MAGIC and Fermi /VERITAS spetra to see if CTA an distinguish them.
intrinsi power law has dierent index: 2.56 ± 0.11 for Fermi, 3.1 ± 0.3 for
MAGIC and 2.99±0.38 for VERITAS. As seen in Figure 9.5, depending on the hoie
Every
made for the intrinsi spetrum, CTA will be able to distinguish whether the power
law index is similar to the MAGIC's or the VERITAS's slope, when extrapolated to
higher energies. This an also be veried in table 9.1, where the spei numbers
derived from Figure 9.5 are shown.
In the simulations, several realisti observational times were tested to establish
when new results would be ahievable.
In order to have better resolution at low
132
Chapter 9. IC 443 in MAGIC stereo and prospets with CTA
Figure 9.5:
CTA simulated spetrum of IC 443 with onguration I (green urve)
and 50 hours.
The input spetra (grey lines) orrespond:
the power law published from
Fermi
at lower energies to
above 3 GeV, whereas at higher energies the
power law index is taken from the measurements by MAGIC and VERITAS. The
grey symbols show the atual data from previous experiments. The simulated data
points for CTA above 100 GeV an be tted to a power law, whih index depends
on the assumed initial spetra (blak dots for MAGIC, blue ones for VERITAS).
9.3. IC443 as seen in CTA
133
Table 9.2: Statistis of two ttings to the spetrum for IC 443, when simulating
CTA response for 20 hrs in onguration I. The simulated data points use the
intrinsi spetra from Figure 9.6: a power law with a ut o at a few TeV. The two
ttings, then, are a power law with or without a ut o. The rst number is the
t probability, whih values should be in the range between
5 − 60%, the losest
2
redued χ (dened
50%, the better. The seond set of numbers represents the
χ2 divided by the number of degrees of freedom), and for a
to
as
good t, it should be
loser to 1.
Cut-o at 5 TeV
Power law t
Power law + ut-o t
Cut-o at 10 TeV
2.21%
9.69%
19.38 / 9
14.79 / 9
61.09%
39.7%
6.38 / 8
8.38 / 8
energies (several GeV), CTA needs at least 20 hours of observation time, independently of the layout of the used onguration. On the other hand, at high energies
(several TeV), CTA needs more than 10 hours to ahieve better results than with
already operating experiments. At these energies, the ompat onguration (B) is
not as useful as the other more extended ongurations (I or D).
Another interesting point fouses on whether CTA ould distinguish the existene of a ut-o in the power law spetrum above the energies of MAGIC and
VERITAS. The last data points measured by ground based telesopes are between
1 and 2 TeV. If a ut-o was to be found lose to this energy, it ould be deteted
easier by an extended onguration as, for example, onguration D (with the best
sensitivity in this energy range). However, a higher ut-o (above 10 TeV) tting
is hard to disriminate from a simple power-law tting, independently of the used
onguration, see Figure 9.6. To obtain enough statistis, more than 20 hours of
observation time are needed. But even in that ase, distinguishing between a powerlaw and a power-law with a ut-o t is not guaranteed, as an be seen in table
9.2.
In onlusion, the prospets of having CTA as the next generation of Cherenkov
telesopes will bring a solution to some interesting physis ases.
In the ase of
the IC 443 spetrum, CTA will be able to present major overage of the spetrum than the one presentely ahieved by MAGIC or VERITAS and with more auray
(improving 10% the error bars). With already merely
20 − 30
hours of observation
time, new and meaningful results ould be ahieved with enough statistis. However,
if a ut-o were to appear above 5 TeV, CTA might not be able to distinguish it
from a simple power-law.
For a better understanding of all its possible spetra
features, an array onguration with an extended distribution but also with big size
telesopes seems more suitable for all this kind of studies (like the onguration I).
The next step leading to an understanding of the neighbourhood around the
134
Chapter 9. IC 443 in MAGIC stereo and prospets with CTA
E2 dN/dE (TeV cm-2 s-1)
expected spectrum (CTA) for IC 443
Fermi, MAGIC, VERITAS
-9
10
power law fit
power law with cutoff (at 5 TeV) fit
-10
10
-11
10
-12
10
-13
10
-14
10
0.01 0.02
0.1
0.2
1
2 3 45
10
20 30
100
energy E(TeV)
expected spectrum (CTA) for IC 443
Fermi, MAGIC, VERITAS
-9
E2 dN/dE (TeV cm-2 s-1)
10
power law fit
power law with cutoff (at 10 TeV) fit
-10
10
-11
10
-12
10
-13
10
-14
10
0.01 0.02
0.1
0.2
1
2 3 45
10
20 30
100
energy E(TeV)
Figure 9.6: The spetrum of IC443 is simulated with layout CTA-I for 50 hours of
observation, assuming an input spetrum in the form of a power law with a ut o of
5 (top) and 10 (bottom) TeV. The power law index is the one published by MAGIC
(-3.1).
The highest energy ut-o that ould be resolved is at 5 TeV, at higher
energies (i.e. 10 TeV) a tting with power law with a ut o (red) is statistially
undistinguishable from a simple power law (green) in the observed CTA range of
energies.
9.3. IC443 as seen in CTA
135
SNR IC 443 will be a morphologial study and an atual hek of a possible energy
dependene.
Chapter 10
Conlusions and future work
10.1 Final remarks
One of the most distinguishing aspets on studies about diuse emission is that
some spetral signatures may serve as an identiation of the underlying mehanism
produing the gamma rays. In other words, they may help to disern whih kind of
aelerator and under whih diusion properties osmi rays (CRs) propagate.
Following the topi on CR diusion, in Chapters 3 and 4, a theoretial model has
been presented explaining the phenomenology around the SNR IC 443 at energies
above 100 MeV, plaing an emphasis on the displaement between the soures at
high and very high energy (HE and VHE respetively). The displaement is generated by the dierent properties of the proton spetrum at dierent loations, i.e.,
how separated are the SNR and the moleular loud in front of it. These dierenes
are produed by the diusion of CRs from the aelerator (IC 443) to the target.
The VHE soure disovered by the MAGIC telesope is interpreted as a delayed
TeV emission of CRs diusing from the SNR. Whereas the HE soure an be explained as produed by the same aelerator, without produing a o-spatial VHE
soure.
Some of the preditions made before the
were orretly fulllen.
Fermi
telesope was launhed
At a morphologial level, when the energy is lower, the
gamma-ray radiation has been deteted loser to the SNR shell. At a spetral level,
suient statistis have shown that the spetrum gets harder when going towards
lower gamma-ray energies.
However, the
Fermi
results have extended the energy domain of the SED muh
beyond what was possible for its predeessor. The spetrum appears harder than
what was previously suggested, presenting an almost at SED up to 10 GeV, with a
roll-over in the spetrum between 10 and 100 GeV. The original parameters of the
model needed a sligth modiation in their values: mainly, the loation and masses of
the overtaken louds. The ombined spetra measured by VHE and
Fermi
telesopes
an be explained in a senario where a giant loud produes a peak at about the
Fermi
spetral turnover.
The distane between the loud and the SNR shell is
smaller than previously predited and the CR are aeted by a faster diusion. The
diusion oeient is lower and the osmi-ray density is higher than the Earthvalues of both magnitudes.
Nonetheless, there are left some unertainties in the
amount and the loalization of the target moleular mass, and the density of this
moleular material.
Those aveats should be addressed in subsequent studies on
this an similar soures, like the southern W28 deteted by H.E.S.S., or the northern
W51C reported by MAGIC and VERITAS.
138
Chapter 10. Conlusions and future work
In Chapter 5, a model for starburst galaxies is presented and suesfully onrmed by the more reent observations. Suh galaxies have an enhanement both
in the star formation and supernova (SN) explosion rate, and dense environments
at their enters. Very energeti gamma rays are produed due to CRs interations
with ambient nulei and subsequent
π0
deay.
The main model desribed multi-
frequeny (from radio to near infrared) and multi-messenger (neutrinos) preditions
for the photon emission oming from the entral region of M82.
The model pre-
sented is onsistent along the eletromagneti spetrum, and allows to trak the
emission to one and the same original osmi-ray population.
This population is
a onsequene of every leptoni and hadroni hannel, inluding both primary and
seondary partiles.
The model explains reasonably well both the HE and VHE
emission oming from the two losest starburst galaxies M82 and NGC 253, within
a range of the explored parameters already mentioned.
Now, the opportunity to
ontinue working in these objets is open, and further studies on CR enhanement,
X-ray preditions, and features in the spetra below 300 GeV and above 1 TeV are
expeted.
10.2 Future work
The Thesis onludes with a few initial studies on key objets with the forthoming
Cherenkov Telesope Array (CTA) in Chapter 8:
•
The ability to distinguish moleular louds illuminated by esaping osmi
rays from a nearby SNR, although the whole V-shape spetrum has to be
obtained by a ombination of
Fermi
and CTA data. The aveats of this study
are a onsequene of the theoretial model behind it: suh large masses for
moleular louds tend to be extended and morphologial studies are required.
Also, a range of unertainty is needed for both distanes and mass of moleular
louds, beause assoiation between SNR and moleular louds gets harder the
wider the separation.
•
Conerning starburst galaxies, a muh better reonstruted spetrum should
be ahieved, ompared to the existing one for M82. Further studies are expeted to report on the possible uto in the proton spetra aroung TeV energies. However, the other andidate from this soure-lass, NGC 253, is not
so easily deteted, therefore an eort should be made towards ahieving an
analysis, like the H.E.S.S model analysis that guaranteed its detetion. One
this is aomplished, diuse radiation from other starburst galaxies plaed
further away may be deteted, so that a population study an be initiated.
•
The study on SNR IC 443 tried to stablish the energy dependene of the
gamma-ray entroid, the photon index of the spetrum and the extension. In
the spetral study it ould be seen that the existing statistis on photon index
were signiantly improved. However, the opposite happened respet to the
10.2. Future work
139
possibility to distinguish a ut-o over few TeVs, where suient statistis
were not ahieved.
CTA will have better sensitivity (one order of magnitud at 1 TeV) and better
angular resolution.
This is right now the future of the ground-based astronomy
at the highest energies. The window will be open to unveil the origin of CR and
the SNR as their main aelerator. On the latter objets, population studies and
spetral studies looking for a ut-o (to disentangle hadroni/leptoni models)
are expeted to beome ommon.
Related with this topi, the natural targets
for these aelerators, the moleular louds nearby, will also be studied.
Other
projets await, like multifrequeny (X-ray, gas) and multi-messenger (neutrinos)
observations
and
models,
together
with
morphologial
and
studies, where a dependeny on the energy might be tested.
extension-related
To avoid the soure
onfussion, more detailed diusion skymaps will be developed. And with respet to
extragalati soures, like the starburst galaxies, extension and morphology will be
explored, apart from detailed spetra and variability tests (like in blazar and other
ative galati nulei objets).
All and all, this Thesis is just the tip of the ieberg: the eld is wide and many
prospets for future work will ontinue to open as our understanding on gammaray astronomy progresses.
The studies presented in this Thesis simply represent
a starting point, and even more exiting topis lay ahead.
begun. . .
The journey has just
Bibliography
[Abdo
et al.
2008℄ A. A. Abdo, M. Akermann, W. B. Atwood, L. Baldini, J. Ballet,
G. Barbiellini, M. G. Baring, D. Bastieri, B. M. Baughman, K. Behtol
The Fermi Gamma-Ray Spae Telesope Disovers the
Pulsar in the Young Galati Supernova Remnant CTA 1. Siene, vol. 322,
and 175 oauthors.
no. 5905, pages 12181221, 2008. (Cited on page 11.)
[Abdo
et al.
2009a℄ A. A. Abdo, M. Akermann, M. Ajello, B. Anderson, W. B.
Atwood, M. Axelsson, L. Baldini, J. Ballet, G. Barbiellini, M. G. Baring
Detetion of 16 Gamma-Ray Pulsars Through Blind
Frequeny Searhes Using the Fermi LAT. Siene, vol. 325, no. 5942, pages
and 170 oauthors.
840844, 2009. (Cited on page 11.)
[Abdo
et al.
2009b℄ A. A. Abdo, M. Akermann, M. Ajello, K. Asano, W. B. At-
wood, M. Axelsson, L. Baldini, J. Ballet, G. Barbiellini, M. G. Baring and
A limit on the variation of the speed of light arising from
quantum gravity eets. Nature, vol. 462, no. 7271, pages 331334, 2009.
199 oauthors.
(Cited on page 13.)
[Abdo
et al.
2009℄ A. A. Abdo, M. Akermann, M. Ajello, W. B. Atwood, M. Ax-
elsson, L. Baldini, J. Ballet, D. L. Band, G. Barbiellini, D. Bastieri and 200
oauthors.
Fermi/Large Area Telesope Bright Gamma-Ray Soure List.
As-
trophysial Journal Supplement, vol. 183, no. 1, pages 4666, 2009. (Cited
on page 101.)
[Abdo
et al.
2009d℄ A. A. Abdo, M. Akermann, M. Ajello, W. B. Atwood, M. Ax-
elsson, L. Baldini, J. Ballet, G. Barbiellini, M. G. Baring, D. Bastieri and
Detetion of 16 Gamma-Ray Pulsars Through Blind Frequeny Searhes Using the Fermi LAT. Siene, vol. 325, no. 5942, pages
192 oauthors.
840844, 2009. (Cited on page 109.)
[Abdo
et al.
2009e℄ A. A. Abdo, M. Akermann, M. Ajello, W. B. Atwood, M. Ax-
elsson, L. Baldini, J. Ballet, G. Barbiellini, M. G. Baring, D. Bastieri and
A Population of Gamma-Ray Milliseond Pulsars Seen with
the Fermi Large Area Telesope. Siene, vol. 325, no. 5942, pages 848852,
192 oauthors.
2009. (Cited on page 11.)
[Abdo
et al.
2009f ℄ A. A. Abdo, M. Akermann, M. Ajello, W. B. Atwood, M. Ax-
elsson, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, B. M. Baughman
Detetion of High-Energy Gamma-Ray Emission from
the Globular Cluster 47 Tuanae with Fermi. Siene, vol. 325, no. 5942,
and 157 oauthors.
pages 844848, 2009. (Cited on page 11.)
142
[Abdo
Bibliography
et al.
2009g℄ A. A. Abdo, M. Akermann, M. Ajello, M. Axelsson, L. Baldini,
J. Ballet, G. Barbiellini, D. Bastieri, B. M. Baughman and 167 oauthors.
Modulated High-Energy Gamma-Ray Emission from the Miroquasar Cygnus
X-3. Siene, vol. 326, no. 5959, pages 15121516, 2009. (Cited on page 10.)
[Abdo
et al.
2009h℄ A. A. Abdo, M. Akermann, M. Arimoto, K. Asano, W. B.
Atwood, M. Axelsson, L. Baldini, J. Ballet, D. L. Band, G. Barbiellini and
Fermi Observations of High-Energy Gamma-Ray Emission
from GRB 080916C. Siene, vol. 323, no. 5922, pages 16881692, 2009.
244 oauthors.
(Cited on page 13.)
[Abdo
et al.
2009i℄ A. A. Abdo, B. T. Allen, T. Aune, D. Berley, C. Chen, G. E.
Christopher, T. DeYoung, B. L. Dingus, R. W. Ellsworth, M. M. Gonzalez
Milagro Observations of Multi-TeV Emission from Galati Soures in the Fermi Bright Soure List. Astrophysial Journal Letters,
and 20 oauthors.
vol. 700, no. 2, pages 127131, 2009.
(Cited on pages 101, 105, 109, 110
and 175.)
[Abdo
et al.
2010a℄ A. A. Abdo, M. Akermann, M. Ajello, A. Allafort, E. Antolini,
W. B. Atwood, M. Axelsson, L. Baldini, J. Ballet, G. Barbiellini and 225
oauthors.
Fermi Large Area Telesope First Soure Catalog.
Astrophysi-
al Journal Supplement, vol. 188, no. 2, pages 405436, 2010.
(Cited on
pages 104, 110 and 175.)
[Abdo
et al.
2010b℄ A. A. Abdo, M. Akermann, M. Ajello, W. B. Atwood, M. Ax-
elsson, L. Baldini, J. Ballet, G. Barbiellini, M. G. Baring, D. Bastieri and
207 oauthors.
Pulsars.
The First Fermi Large Area Telesope Catalog of Gamma-ray
Astrophysial Journal Supplement, vol. 187, no. 2, pages 460494,
2010. (Cited on pages 109, 110 and 175.)
[Abdo
et al.
2010℄ A. A. Abdo, M. Akermann, M. Ajello, W. B. Atwood, M. Ax-
elsson, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, K. Behtol and 161
Detetion of Gamma-Ray Emission from the Starburst Galaxies
M82 and NGC 253 with the Large Area Telesope on Fermi. The Astrooauthors.
physial Journal Letters, vol. 709, no. 2, pages L152L157, 2010. (Cited on
pages 13, 58, 74 and 118.)
[Abdo
et al.
2010d℄ A. A. Abdo, M. Akermann, M. Ajello, W. B. Atwood, L. Bal-
dini, J. Ballet, G. Barbiellini, D. Bastieri, B. M. Baughman, K. Behtol and
172 oauthors.
Fermi Gamma-Ray Imaging of a Radio Galaxy.
Siene,
vol. 328, no. 5979, pages 725728, 2010. (Cited on page 12.)
[Abdo
et al.
2010e℄ A. A. Abdo, M. Akermann, M. Ajello, W. B. Atwood, L. Bal-
dini, J. Ballet, G. Barbiellini, D. Bastieri, K. Behtol, R. Bellazzini and 206
Gamma-Ray Emission Conurrent with the Nova in the Symbioti Binary V407 Cygni. Siene, vol. 329, no. 5993, pages 817821, 2010.
oauthors.
(Cited on page 9.)
Bibliography
[Abdo
et al.
143
2010f ℄ A. A. Abdo, M. Akermann, M. Ajello, L. Baldini, J. Ballet,
G. Barbiellini, M. G. Baring, D. Bastieri, B. M. Baughman, K. Behtol and
171 oauthors. Gamma-Ray Emission from the Shell of Supernova Remnant
W44 Revealed by the Fermi LAT. Siene, vol. 327, no. 5969, pages 1103
1106, 2010. (Cited on pages 9 and 169.)
[Abdo
et al.
2010g℄ A. A. Abdo, M. Akermann, M. Ajello, L. Baldini, J. Ballet,
G. Barbiellini, D. Bastieri, B. M. Baughman, K. Behtol, R. Bellazzini and
Observation of Supernova Remnant IC 443 with the Fermi
Large Area Telesope. Astrophysial Journal, vol. 712, no. 1, pages 459468,
162 oauthors.
2010. (Cited on pages 42, 43, 45, 127 and 177.)
[Abdo
et al.
2010h℄ A. A. Abdo, M. Akermann, M. Ajello, L. Baldini, J. Ballet,
G. Barbiellini, D. Bastieri, B. M. Baughman, K. Behtol, R. Bellazzini and
PSR J1907+0602: A Radio-Faint Gamma-Ray Pulsar Powering a Bright TeV Pulsar Wind Nebula. The Astrophysial Journal, vol. 711,
170 oauthors.
no. 1, pages 6474, 2010. (Cited on page 43.)
[Abdo
et al.
2010i℄ A.
A.
Abdo,
D.
Parent,
J.
E.
Grove,
G.
A.
Caliandro,
Fermi LAT Detetion of
GeV Gamma-Ray Emission from the Binary System PSRB1259-63. The
M. Roberts, S. Johnston and M. Chernyakova.
Astronomer's Telegram, vol. 3085, pages 1+, 2010. (Cited on page 10.)
[Abdo
et al.
2011℄ A. A. Abdo, M. Akermann, M. Ajello, A. Allafort, L. Baldini,
J. Ballet, G. Barbiellini, D. Bastieri, K. Behtol, R. Bellazzini and 158 oauthors.
Gamma-Ray Flares from the Crab Nebula.
Siene, vol. 331, no. 6018,
pages 739742, 2011. (Cited on page 10.)
[Aiari
et al.
2009a℄ V. A. Aiari, E. Aliu, T. Arlen, T. Aune, M. Bautista,
M. Beilike, W. Benbow, D. Boltuh, S. M. Bradbury and 83 oauthors.
A onnetion between star formation ativity and osmi rays in the starburst galaxy M82. Nature, vol. 462, no. 7274, pages 770772, 2009. (Cited
on pages 13, 74 and 118.)
[Aiari
et al.
2009b℄ V. A. Aiari, E. Aliu, T. Arlen, T. Aune, M. Bautista,
M. Beilike, W. Benbow, S. M. Bradbury, J. H. Bukley, V. Bugaev and
Observation of Extended Very High Energy Emission from the
Supernova Remnant IC 443 with VERITAS. Astrophysial Journal Letters,
82 oauthors.
vol. 698, no. 2, pages L133L137, 2009. (Cited on page 41.)
[Aiari
et al.
2009℄ V. A. Aiari, E. Aliu, T. Arlen, M. Bautista, M. Beilike,
W. Benbow, S. M. Bradbury, J. H. Bukley, V. Bugaev, Y. Butt and 383
Radio Imaging of the Very-High-Energy γ -Ray Emission Region
in the Central Engine of a Radio Galaxy. Siene, vol. 325, no. 5939, pages
oauthors.
444447, 2009. (Cited on page 12.)
144
[Aero
Bibliography
et al.
2009℄ F. Aero, F. Aharonian, A. G. Akhperjanian, G. Anton, U. Bar-
res de Almeida, A. R. Bazer-Bahi, Y. Beherini, B. Behera, K. Bernlöhr,
Detetion of Gamma Rays from a Starburst Galaxy.
and 161 oauthors.
ene, vol. 326, no. 5956, pages 10801082, 2009.
Si-
(Cited on pages 13, 118
and 120.)
On the emissivity
of π 0 -deay gamma radiation in the viinity of aelerators of galati osmi
rays. Astronomy and Astrophysis, vol. 309, pages 917928, 1996. (Cited on
[Aharonian & Atoyan 1996℄ F. A. Aharonian and A.M. Atoyan.
pages 20, 21, 22, 35, 45, 51, 52, 53 and 172.)
[Aharonian
et al.
2003℄ F. Aharonian, A. Akhperjanian, M. Beilike, K. Bernlöhr,
H.-G. Börst, H. Bojahr, O. Bolz, T. Coarasa, J. L. Contreras, J. Cortina
and 43 oauthors.
ter?
Is the giant radio galaxy M 87 a TeV gamma-ray emit-
Astronomy and Astrophysis, vol. 403, pages L1L5, 2003. (Cited on
page 12.)
[Aharonian
et al.
2004a℄ F. A. Aharonian, A. G. Akhperjanian, K.-M. Aye, A. R.
Bazer-Bahi, M. Beilike, W. Benbow, D. Berge, P. Berghaus, K. Bernlhr,
O. Bolz and 90 oauthors.
supernova remnant.
High-energy partile aeleration in the shell of a
Nature, vol. 432, no. 7013, pages 7577, 2004. (Cited
on page 122.)
[Aharonian
et al.
2004b℄ F. A. Aharonian, A. G. Akhperjanian, K.-M. Aye, A. R.
Bazer-Bahi, M. Beilike, W. Benbow, D. Berge, P. Berghaus, K. Bernlöhr,
O. Bolz and 90 oauthors.
supernova remnant.
High-energy partile aeleration in the shell of a
Nature, vol. 432, no. 7013, pages 7577, 2004. (Cited
on pages 9 and 169.)
[Aharonian
et al.
2005a℄ F. Aharonian, A. G. Akhperjanian, K.-M. Aye, A. R.
Bazer-Bahi, M. Beilike, W. Benbow, D. Berge, P. Berghaus, K. Bernlöhr,
Disovery of the binary pulsar PSR B1259-63
in very-high-energy gamma rays around periastron with HESS. Astronomy
C. Boisson and 92 oauthors.
and Astrophysis, vol. 442, pages 110, 2005. (Cited on page 10.)
[Aharonian
et al.
2005b℄ F. A. Aharonian, A. G. Akhperjanian, K.-M. Aye, A. R.
Bazer-Bahi, M. Beilike, W. Benbow, D. Berge, P. Berghaus, K. Bern-
A New Population of Very High Energy
Gamma-Ray Soures in the Milky Way. Siene, vol. 307, no. 5717, pages
löhr, C. Boisson and 90 oauthors.
19381942, 2005. (Cited on page 10.)
[Aharonian
et al.
2005℄ F. A. Aharonian, A. G. Akhperjanian, K.-M. Aye, A. R.
Bazer-Bahi, M. Beilike, W. Benbow, D. Berge, P. Berghaus, K. Bernlöhr,
Disovery of Very High Energy Gamma Rays
Assoiated with an X-ray Binary. Siene, vol. 309, no. 5735, pages 746749,
C. Boisson and 93 oauthors.
2005. (Cited on page 10.)
Bibliography
[Aharonian
et al.
145
2006a℄ F. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bahi,
M. Beilike, W. Benbow, D. Berge, K. Bernlhr, C. Boisson, O. Bolz, V. Borrel
and 97 oauthors.
Observations of the Crab nebula with HESS.
Astronomy
and Astrophysis, vol. 457, no. 3, pages 899915, 2006. (Cited on page 120.)
[Aharonian
et al.
2006b℄ F. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bahi,
M. Beilike, W. Benbow, D. Berge, K. Bernlöhr, C. Boisson, O. Bolz, V. Borrel and 105 oauthors. Energy dependent γ−ray morphology in the pulsar
wind nebula HESS J1825-137. Astronomy and Astrophysis, vol. 460, no. 2,
pages 365374, 2006. (Cited on page 43.)
[Aharonian
et al.
2006℄ F. A. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bahi,
M. Beilike, W. Benbow, D. Berge, K. Bernlhr, C. Boisson, O. Bolz, V. Borrel
First detetion of a VHE gamma-ray spetral maximum
from a osmi soure: HESS disovery of the Vela X nebula. Astronomy and
and 96 oauthors.
Astrophysis, vol. 448, no. 2, pages L43L47, 2006. (Cited on page 25.)
[Aharonian
et al.
2006d℄ F. A. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bahi,
M. Beilike, W. Benbow, D. Berge, K. Bernlöhr, C. Boisson, O. Bolz, V. Borrel and 113 oauthors.
the Radio Galaxy M87.
Fast Variability of Tera-Eletron Volt γ Rays from
Siene, vol. 314, no. 5804, pages 14241427, 2006.
(Cited on page 12.)
[Aharonian
et al.
2006e℄ F. A. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bahi,
M. Beilike, W. Benbow, D. Berge, K. Bernlöhr, C. Boisson, O. Bolz, V. Borrel and 92 oauthors.
Centre ridge.
Disovery of very-high-energy γ -rays from the Galati
Nature, vol. 439, no. 7077, pages 695698, 2006.
(Cited on
page 10.)
[Aharonian
et al.
2006f ℄ F. A. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bahi,
M. Beilike, W. Benbow, D. Berge, K. Bernlöhr, C. Boisson, O. Bolz, V. Bor-
A low level of extragalati bakground light as revealed
by γ -rays from blazars. Nature, vol. 440, no. 7087, pages 10181021, 2006.
rel and 92 oauthors.
(Cited on page 11.)
[Aharonian
et al.
2009℄ F. A. Aharonian, A. G. Akhperjanian, G. Anton, U. Bar-
res de Almeida, A. R. Bazer-Bahi, Y. Beherini, B. Behera, W. Benbow,
Detetion of very high energy
radiation from HESS J1908+063 onrms the Milagro unidentied soure
MGRO J1908+06. Astronomy and Astrophysis, vol. 499, no. 3, pages 723
K. Bernlöhr, C. Boisson and 149 oauthors.
728, 2009. (Cited on page 43.)
[Aharonian 2001℄ F. A. Aharonian.
Gamma Rays From Moleular Clouds.
Spae
Siene Review, vol. 99, no. 1, pages 187196, 2001. (Cited on page 122.)
[Akyüz
et al.
1991℄ A. Akyüz, A. Brouillet and M.E. Özel.
M82 in gamma-rays.
Astronomy and Astrophysis, vol. 248, no. 2, pages 419420, 1991. (Cited
on page 63.)
146
Bibliography
et al.
[Albert
2006℄ J. Albert, E. Aliu, H. Anderhub, P. Antoranz, A. Armada,
M. Asensio, C. Baixeras, J. A. Barrio, M. Bartelt, H. Bartko and 138 oauthors. Variable Very-High-Energy Gamma-Ray Emission from the Miroquasar LS I +61 303. Siene, vol. 312, no. 5781, pages 17711773, 2006.
(Cited on page 10.)
et al.
[Albert
2007a℄ J. Albert, E. Aliu, H. Anderhub, P. Antoranz, A. Armada,
C. Baixeras, J. A. Barrio, H. Bartko, D. Bastieri, J. K. Beker and 130
Very High Energy Gamma-Ray Radiation from the Stellar Mass
Blak Hole Binary Cygnus X-1. The Astrophysial Journal, vol. 665, pages
oauthors.
L51L54, 2007. (Cited on page 10.)
et al.
[Albert
2007b℄ J. Albert, E. Aliu, H. Anderhub, P. Antoranz, A. Armada,
C. Baixeras, J. A. Barrio, H. Bartko, D. Bastieri, J. K. Beker and 131
Disovery of Very High Energy Gamma Radiation from IC 443
with the MAGIC Telesope. Astrophysial Journal, vol. 664, no. 2, pages
oauthors.
L87L90, 2007. (Cited on pages 34, 35, 125, 126 and 177.)
et al.
[Albert
2007℄ J. Albert, E. Aliu, H. Anderhub, P. Antoranz, A. Armada,
C. Baixeras, J. A. Barrio, H. Bartko, D. Bastieri, J. K. Beker and 134
oauthors.
Unfolding of dierential energy spetra in the MAGIC experiment.
Nulear Instruments and Methods in Physis Researh A, vol. 583, pages
494506, 2007. (Cited on page 99.)
et al.
[Albert
2008a℄ J. Albert, E. Aliu, H. Anderhub, L. A. Antonelli, P. Antoranz,
VeryHigh-Energy gamma rays from a Distant Quasar: How Transparent Is the
Universe? Siene, vol. 320, no. 5884, pages 17521754, 2008. (Cited on
M. Bakes, C. Baixeras, J. A. Barrio, H. Bartko and 140 oauthors.
page 12.)
et al.
[Albert
2008b℄ J. Albert, E. Aliu, H. Anderhub, P. Antoranz, A. Armada,
C. Baixeras, J. A. Barrio, H. Bartko, D. Bastieri, J. K. Beker and 132
VHE -Ray Observation of the Crab Nebula and its Pulsar with
the MAGIC Telesope. Astrophysial Journal, vol. 674, no. 2, pages 1037
oauthors.
1055, 2008. (Cited on pages 106, 110 and 175.)
[Aleksi¢
et al.
2010℄ J. Aleksi¢, L. A. Antonelli, P. Antoranz, M. Bakes, J. A. Bar-
rio, D. Bastieri, J. Beerra González, W. Bednarek, A. Berdyugin, K. Berger
MAGIC Upper Limits for two Milagro-deteted, Bright
Fermi Soures in the Region of SNR G65.1+0.6. Astrophysial Journal,
and 137 oauthors.
vol. 725, no. 2, pages 16291632, 2010. (Cited on pages 16, 103 and 130.)
[Aliu
et al.
2008a℄ E. Aliu, H. Anderhub, L. A. Antonelli, P. Antoranz, M. Bakes,
C. Baixeras, J. A. Barrio, H. Bartko, D. Bastieri, J. K. Beker and 139
Observation of Pulsed -Rays Above 25 GeV from the Crab Pulsar
with MAGIC. Siene, vol. 322, no. 5905, page 1221, 2008. (Cited on page 91.)
oauthors.
Bibliography
[Aliu
et al.
147
2008b℄ E. Aliu, H. Anderhub, L. A. Antonelli, P. Antoranz, M. Bakes,
C. Baixeras, J. A. Barrio, H. Bartko, D. Bastieri, J. K. Beker and 139
oauthors. Observation of Pulsed γ -Rays Above 25 GeV from the Crab Pulsar
with MAGIC. Siene, vol. 322, no. 5905, pages 12211223, 2008. (Cited on
page 11.)
[Aliu
et al.
2009℄ E. Aliu, H. Anderhub, L. A. Antonelli, P. Antoranz, M. Bakes,
C. Baixeras, J. A. Barrio, H. Bartko, D. Bastieri, J. K. Beker and 137
Improving the performane of the single-dish Cherenkov telesope
MAGIC through the use of signal timing. Astropartile Physis, vol. 30, no. 6,
oauthors.
pages 293305, 2009. (Cited on page 96.)
[Anhordoqui
et al.
2003℄ L. A. Anhordoqui, D. F. Torres, T. P. MCauley, G. E.
Romero and F. A. Aharonian.
Neutrinos from Areting Neutron Stars.
The Astrophysial Journal, vol. 589, no. 1, pages 481486, 2003. (Cited on
page 55.)
et al. 2004℄ L.A. Anhordoqui, H. Goldberg, F. Halzen and T. J.
Weiler. Neutrino bursts from Fanaro Riley I radio galaxies. Physis Letters
[Anhordoqui
B, vol. 600, no. 3-4, pages 202207, 2004. (Cited on page 73.)
et al. 2008℄ L.A. Anhordoqui, D. Hooper, S. Sarkar and A. M. TayHigh energy neutrinos from astrophysial aelerators of osmi ray nu-
[Anhordoqui
lor.
lei.
Astropartile Physis, vol. 29, no. 1, pages 113, 2008.
(Cited on
pages 57 and 73.)
CO observations of IRAS Cirular No. 9 soures 19520 + 2759 and 01133 + 6434 - Regions of star formation. Astronomy and Astrophysis, vol. 173, no. 2, pages 271278, 1987.
[Arquilla & Kwok 1987℄ R. Arquilla and S. Kwok.
(Cited on page 103.)
An X-ray study of
IC443 and the disovery of a new supernova remnant by ROSAT. Astronomy
[Asaoka & Ashenbah 1994℄ I. Asaoka and B. Ashenbah.
and Astrophysis, vol. 284, no. 2, pages 573582, 1994. (Cited on page 33.)
et al. 1995℄ A. M. Atoyan, F. A. Aharonian and H. J. Völk. Eletrons and
positrons in the galati osmi rays. Physial Review D (Partiles, Fields,
[Atoyan
Gravitation, and Cosmology), vol. 52, no. 6, pages 32653275, 1995. (Cited
on page 21.)
[Baring
et al.
1999℄ M. G. Baring, D. C. Ellison, S. P. Reynolds, I. A. Grenier and
P. Goret. Radio to Gamma-Ray Emission from Shell-Type Supernova Remnants: Preditions from Nonlinear Shok Aeleration Models. The Astrophysial Journal, vol. 513, no. 1, pages 311338, 1999. (Cited on page 19.)
[Bartel
et al.
1987℄ N. Bartel, M. I. Ratner, A. E. E. Rogers, I. I. Shapiro, R. J.
Bonometti, N. L. Cohen, M. V. Gorenstein, J. M. Maraide and R. A. Pre-
148
Bibliography
ston.
VLBI observations of 23 hot spots in the starburst galaxy M82.
Astro-
physial Journal, vol. 323, no. 1, pages 505515, 1987. (Cited on page 66.)
[Bartko & Bednarek 2008℄ H. Bartko and W. Bednarek.
PWNe interating with moleular louds.
Gamma-ray emission from
Monthly Noties of the Royal As-
tronomial Soiety, vol. 385, no. 3, pages 11051109, 2008. (Cited on pages 39
and 43.)
[Bazo Alba
et al.
2009℄ J. L. Bazo Alba, R. Abbasi, Y. Abdou, M. Akermann,
J. Adams, J. Aguilar, M. Ahlers, K. Andeen, J. Auenberg, X. Bai, M. Baker
and 240 oauthors.
Searh for neutrino point soures with IeCube 22-strings.
Nulear Physis B Proeedings Supplements, vol. 188, pages 267269, 2009.
(Cited on page 73.)
Revised equipartition and minimum
energy formula for magneti eld strength estimates from radio synhrotron
observations. Astronomishe Nahrihten, vol. 326, no. 6, pages 414427,
[Bek & Krause 2005℄ R. Bek and M. Krause.
2005. (Cited on pages 71 and 72.)
[Beker 2008℄ J. K. Beker.
astrophysis.
High-energy neutrinos in the ontext of multimessenger
Physis Reports, pages 173246, Marh 2008. (Cited on pages 2
and 169.)
[Bell 1978℄ A. R. Bell.
The aeleration of osmi rays in shok fronts. II.
Monthly
Noties of Royal Astronomial Soiety, vol. 182, pages 443455, 1978. (Cited
on pages 19 and 61.)
et al. 2006℄ E. G. Berezhko, L. T. Ksenofontov and H. J. Völk. Gammaray emission expeted from Kepler's supernova remnant. Astronomy and
[Berezhko
Astrophysis, vol. 452, no. 1, pages 217221, 2006. (Cited on page 61.)
[Berezinskii
et al.
Ptuskin.
1990℄ V. S. Berezinskii, S. V. Bulanov, V. A. Dogiel and V. S.
Ginzburg, V. L., Amsterdam, North-Holland, 1990.
(Cited on
pages 50 and 62.)
[Bertsh
et al.
1993℄ D. L. Bertsh, T. M. Dame, C. E. Fihtel, S. D. Hunter,
Diuse Gamma-Ray Emission
in the Galati Plane from Cosmi-Ray, Matter, and Photon Interations.
P. Sreekumar, J. G. Stay and P. Thaddeus.
Astrophysial Journal, vol. 416, pages 587600, 1993. (Cited on page 20.)
[Blattnig
et al.
2000a℄ S. R. Blattnig, S. R. Swaminathan, A. T. Kruger, M. Ngom
Parametrizations of inlusive ross setions for pion
prodution in proton-proton ollisions. Physial Review D, id.094030, vol. 62,
and J. W. Norbury.
no. 9, 2000. (Cited on page 51.)
[Blattnig
et al.
2000b℄ S. R. Blattnig, S. R. Swaminathan, A. T. Kruger, M. Ngom,
J. W. Norbury and R. K. Tripathi.
Parameterized Cross Setions for Pion
Bibliography
149
Prodution in Proton-Proton Collisions.
Tehnial Report, NASA/TP-2000-
210640, vol. 1, 2000. (Cited on page 51.)
[Blom
et al. 1999℄ J. J. Blom, T. A. Paglione and A. Carramiñana. Diuse GammaRay Emission from Starburst Galaxies and M31. The Astrophysial Journal,
vol. 516, no. 2, pages 744749, 1999. (Cited on pages 57 and 59.)
[Bohino & Bykov 2000℄ F. Bohino and A. M. Bykov.
IC443: evidene for a shoked moleular lump?
Hard X-ray emission from
Astronomy and Astro-
physis, vol. 362, pages L29L32, 2000. (Cited on page 33.)
[Bohino & Bykov 2001℄ F. Bohino and A. M. Bykov.
443: The XMM-Newton view.
The plerion nebula in IC
Astronomy and Astrophysis, vol. 376, pages
248253, 2001. (Cited on pages 33, 39 and 125.)
[Bohino & Bykov 2003℄ F. Bohino and A. M. Bykov.
hard X-ray soures in IC 443.
XMM-Newton study of
Astronomy and Astrophysis, vol. 400, pages
203211, 2003. (Cited on page 33.)
The struture and dynamis of
evolved supernova remnants - The IC 443 omplex. Astronomy and Astro-
[Braun & Strom 1986℄ R. Braun and R. G. Strom.
physis, vol. 164, no. 1, pages 193207, 1986. (Cited on page 31.)
et al. 2002℄ A. Bressan, L. Silva and G. L. Granato. Far infrared and radio
emission in dusty starburst galaxies. Astronomy and Astrophysis, vol. 392,
[Bressan
pages 377391, 2002. (Cited on page 68.)
[Brown & Marsher 1977℄ R. L. Brown and A. P. Marsher.
eletrons in dense interstellar louds.
Energeti seondary
Astrophysial Journal, vol. 212, no. 1,
pages 659663, 1977. (Cited on page 59.)
[Butt
et al.
2003℄ Y. M. Butt, D. F. Torres, J. A. Combi, T. Dame and G. E.
Moleular Beam Dumps as Traers of Hadroni Cosmi Ray
Soures: the Case of SNR IC 443. In XXIInd Moriond Astrophysis Meet-
Romero.
ing, pages 323331. arXiv:astro-ph/0206132v2, 2003. (Cited on pages 33, 37
and 45.)
[Bykov
et al. 2000℄ A. M. Bykov, R. A. Chevalier, D. C. Ellison and Yu. A. Uvarov.
Nonthermal Emission from a Supernova Remnant in a Moleular Cloud.
The Astrophysial Journal, vol. 538, no. 1, pages 203216, 2000.
(Cited
on page 37.)
[Bykov
et al. 2005℄ A. M. Bykov, F. Bohino and G. G. Pavlov. A Hard Extended
X-Ray Soure in the IC 443 Supernova Remnant Resolved by Chandra: A
Fast Ejeta Fragment or a New Pulsar Wind Nebula? The Astrophysial
Journal, vol. 624, no. 1, pages L41L44, 2005. (Cited on page 33.)
150
Bibliography
et al.
[Bykov
2008℄ A. M. Bykov, A. M. Krassilhthikov, Yu. A. Uvarov, H. Bloe-
Isolated
X-Ray-Infrared Soures in the Region of Interation of the Supernova Remnant IC 443 with a Moleular Cloud. The Astrophysial Journal, vol. 676,
men, F. Bohino, G. M. Dubner, E. B. Giaani and G. G. Pavlov.
no. 2, pages 10501063, 2008. (Cited on page 33.)
Free-free absorption towards the nuleus of NGC 253:
further evidene for high pressures in the starburst nuleus. Astronomy and
[Carilli 1996℄ C. L. Carilli.
Astrophysis, vol. 305, pages 402, 1996. (Cited on pages 77 and 174.)
[Casanova
et al.
2010℄ S. Casanova, F. A. Aharonian, Y. Fukui, S. Gabii, D. I.
Jones, A. Kawamura, T. Onishi, G. Rowell, H. Sano, K. Torii and H. Yamamoto.
Moleular Clouds as Cosmi-Ray Barometers.
Publiations of the
Astronomial Soiety of Japan, vol. 62, no. 3, pages 769777, 2010. (Cited
on pages 19 and 122.)
et al. 2004℄ V. Casasola, D. Bettoni and G. Galletta. The gas ontent of
peuliar galaxies: Strongly interating systems. Astronomy and Astrophysis,
[Casasola
vol. 422, pages 941950, 2004. (Cited on page 63.)
et al. 2006℄ V. Cavasinni, D. Grasso and L. Maione. TeV neutrinos
from supernova remnants embedded in giant moleular louds. Astropartile
[Cavasinni
Physis, vol. 26, no. 1, pages 4149, 2006. (Cited on page 55.)
[Cherenkov 1934℄ P. A. Cherenkov.
gamma radiation.
Visible emission of lean liquids by ation of
Doklady Akademii Nauk SSSR Ser. A, vol. 2, pages 451
455, 1934. (Cited on page 84.)
[Chevalier 1999℄ R. A. Chevalier.
Supernova Remnants in Moleular Clouds.
Astrophysial Journal, vol. 511, no. 2, pages 798811, 1999.
The
(Cited on
page 33.)
[Cillis
et al. 2005℄ A. N. Cillis, D. F. Torres and O. Reimer. EGRET Upper Limits
and Staking Searhes of Gamma-Ray Observations of Luminous and Ultraluminous Infrared Galaxies. The Astrophysial Journal, vol. 621, no. 1, pages
139145, 2005. (Cited on page 69.)
et al. 1997℄ M. J. Claussen, D. A. Frail, W. M. Goss and R. A. Gaume.
Polarization Observations of 1720 MHz OH Masers toward the Three Supernova Remnants W28, W44, and IC 443. Astrophysial Journal, vol. 489,
[Claussen
pages 143159, 1997. (Cited on page 31.)
[Corbet
et al.
2011℄ R. H. D. Corbet, C. C. Cheung, M. Kerr, R. Dubois, D. Do-
nato, G. A. Caliandro, M. J. Coe, P. G. Edwards, M. D. Filipovi, J. L.
Payne and J. Stevens.
1FGL J1018.6-5856: a New Gamma-ray Binary.
The
Astronomer's Telegram, vol. 3221, pages 1+, 2011. (Cited on page 10.)
Bibliography
151
et al. 1977℄ R. H. Cornett, G. Chin and G. R. Knapp. Observations of CO
emission from a dense loud assoiated with the supernova remnant IC 443.
[Cornett
Astronomy and Astrophysis, vol. 54, no. 3, pages 889894, 1977. (Cited on
pages 33, 34 and 44.)
[Cortina
et al.
2009℄ J. Cortina, F. Goebel, T. Shweizer and for the MAGIC Col-
laboration.
Tehnial Performane of the MAGIC Telesopes.
In Pro.
31st International Cosmi Ray Conferene. (Šód¹, Poland). arXiv: astroph/0907.1211v1, 2009. (Cited on pages 90 and 174.)
et al. 1978℄ R. M. Cruther, D. H. Rogstad and K. Chu. Aperturesynthesis observations of H I in the galaxy M82. Astrophysial Journal,
[Cruther
vol. 225, no. 1, pages 784789, 1978. (Cited on page 63.)
[Cruther 1988℄ R. M. Cruther.
Dikman, R. and Snell, R. and Young, J. Eds.,
New York, Springer, 1988. (Cited on page 68.)
Clouds, ores and low mass stars. In Proeedings
of the 4th Haystak Observatory, volume 65 of Astronomial Soiety of the
Pai Conferene Series, page 87. Clemens, D. P. and Barvainis, R., 1994.
[Cruther 1994℄ R. M. Cruther.
(Cited on page 68.)
[Cruther 1999℄ R. M. Cruther.
Confront Theory.
Magneti Fields in Moleular Clouds: Observations
The Astrophysial Journal, vol. 520, no. 2, pages 706713,
1999. (Cited on page 68.)
Reent results from VHE gamma astrophysis
related to fundamental physis and osmi rays. ArXiv e-prints, 2011. (Cited
[De Angelis 2011℄ A. De Angelis.
on pages 8 and 179.)
[de Cea del Pozo
et al.
2009a℄ E. de Cea del Pozo, D. F. Torres, A. Y. Rodríguez
Model analysis of the very high energy detetions of the
starburst galaxies M82 and NGC 253. In Pro. 1st Fermi Symposium (Washand O. Reimer.
ington, DC). arXiv: astro-ph/0912.3497v2, 2009.
(Cited on pages 16, 58,
119, 120 and 176.)
[de Cea del Pozo
et al.
2009b℄ E. de Cea del Pozo, D. F. Torres and A. Y. Ro-
dríguez Marrero.
Multi-messenger model for the starburst galaxy M82.
Astrophysial Journal, vol. 698, no. 2, pages 10541071, 2009.
The
(Cited on
pages 16, 58, 75, 76, 118, 120, 174 and 179.)
et al. 2001℄ R. de Grijs, R.
Fossil Starburst in M82. The
[de Grijs
W. O'Connell and J. S. III Gallagher.
The
Astronomial Journal, vol. 121, no. 2, pages
768792, 2001. (Cited on page 66.)
[de Jager & Djannati-Ataï 2009℄ O.C. de Jager and A. Djannati-Ataï.
stars and pulsars, volume 357.
Neutron
Astrophysis and Spae Siene Library,
(Berlin) Springer, 2009. (Cited on page 110.)
152
Bibliography
A high performane
likelihood reonstrution of -rays for imaging atmospheri Cherenkov telesopes. Astropartile Physis, vol. 32, no. 5, pages 231252, 2009. (Cited on
[de Naurois & Rolland 2009℄ M. de Naurois and L. Rolland.
page 120.)
[De Noyer & Frerking 1981℄ L. K. De Noyer and M. A. Frerking.
on shok hemistry in IC 443.
Some new results
Astrophysial Journal, vol. 246, pages L37
L40, 1981. (Cited on pages 33 and 44.)
Seondary prodution of neutral pi-mesons and the
diuse galati gamma radiation. Astronomy and Astrophysis, vol. 157,
[Dermer 1986℄ C. D. Dermer.
no. 2, pages 22322, 1986. (Cited on page 46.)
et al. 1992℄ R. L. Dikman, R. L. Snell, L. M. Ziurys and Y.-L. Huang.
Struture and kinematis of dense gas assoiated with the supernova remnant
IC 443. Astrophysial Journal, vol. 400, no. 1, pages 203213, 1992. (Cited
[Dikman
on pages 33, 34 and 44.)
Manifestations of osmi ray
aeleration in giant moleular louds. Astronomy and Astrophysis, vol. 229,
[Dogel & Sharov 1990℄ V. A. Dogel and G. S. Sharov.
no. 1, pages 259271, 1990. (Cited on page 19.)
[Domingo-Santamaría & Torres 2005℄ E. Domingo-Santamaría and D. F. Torres.
High energy -ray emission from the starburst nuleus of NGC 253. Astronomy
and Astrophysis, vol. 444, no. 2, pages 403415, 2005. (Cited on pages 20,
51, 57, 58, 61, 63, 68, 74, 78, 79, 118, 174 and 179.)
[Domingo-Santamaría
et al.
2005℄ E. Domingo-Santamaría, J. Flix, J. Rio, V. Sal-
zotto and W. Wittek. The DISP analysis method for point-like or extended
gamma soure searhes/studies with the MAGIC Telesope. In Pro. of the
29th International Cosmi Ray Conferene, Pune (India), volume 5, page
363. Mumbai:
Tata Institute of Fundamental Researh, 2005.
(Cited on
page 99.)
[Drury
et al. 1994℄ L. O'C. Drury, F. A. Aharonian and H. J. Völk. The gamma-ray
visibility of supernova remnants. A test of osmi ray origin. Astronomy and
Astrophysis, vol. 287, pages 959971, 1994. (Cited on pages 19 and 59.)
[Elias
et al.
1978℄ J. H. Elias, D. J. Ennis, D. Y. Gezari, M. G. Hauser, J. R. Houk,
K. Y. Lo, K. Matthews, D. Naduea, G. Neugebauer, M. W. Werner and W. E.
Westbrook.
1 millimeter ontinuum observations of extragalati objets.
Astrophysial Journal, vol. 220, no. 1, pages 2541, 1978. (Cited on pages 77
and 174.)
Disovery of very high energy gamma-ray emission
from 3C 279 and 3C 66A/B with the MAGIC telesope. PhD thesis, Univ.
[Errando 2009℄ M. Errando.
Autonoma de Barelona, 2009. (Cited on pages 97 and 175.)
Bibliography
[Everett
et al.
153
2008℄ J. E. Everett, E. G. Zweibel, R. A. Benjamin, D. MCammon,
The Milky Way's Kiloparse-Sale Wind:
A Hybrid Cosmi-Ray and Thermally Driven Outow. The Astrophysial
L. Roks and J. S. III Gallagher.
Journal, vol. 674, no. 1, pages 258270, 2008. (Cited on page 59.)
A Kinship Between the EGRET
Supernova Remnants and Sagittarius A East. The Astrophysial Journal,
[Fatuzzo & Melia 2003℄ M. Fatuzzo and F. Melia.
vol. 596, no. 2, pages 10351043, 2003. (Cited on page 59.)
[Fazio 1967℄ G. G. Fazio.
Gamma Ratiation from Celestial Objets.
Annual Review
of Astronomy and Astrophysis, vol. 5, page 481, 1967. (Cited on page 59.)
[Fesen & Kirshner 1980℄ R. A. Fesen and R. P. Kirshner.
supernova remnant IC 443.
Spetrophotometry of the
Astrophysial Journal, vol. 242, no. 1, pages
10231040, 1980. (Cited on page 31.)
et al.
[Fihtel
1976℄ C. E. Fihtel, D. A. Knien, D. J. Thompson, G. F. Bignami
Signiane of medium-energy gamma-ray astronomy
in the study of osmi rays. Astrophysial Journal, vol. 208, no. 1, pages
and C. Y. Cheung.
211219, 1976. (Cited on page 20.)
[Fomin
et al.
1994℄ V. P. Fomin, A. A. Stepanian, R. C. Lamb, D. A. Lewis,
New methods of atmospheri Cherenkov imaging
for gamma-ray astronomy. I. The false soure method. Astropartile Physis,
M. Punh and T. C. Weekes.
vol. 2, no. 2, pages 137150, 1994. (Cited on pages 91 and 103.)
[Förster
et al.
2003℄ N.M. Förster, M. Sauvage, V. Charmandaris,
P. Gallais, I. F. Mirabel and L. Vigroux.
ies M82, NGC253, and NGC1808.
O. Laurent,
ISOCAM view of the starburst galax-
Astronomy and Astrophysis, vol. 399,
pages 833855, 2003. (Cited on pages 66 and 173.)
[Freedman
et al.
1994℄ W. L. Freedman, S. M. Hughes, B. F. Madore, J. R. Mould,
M. G. Lee, P. Stetson, R. C. Kenniutt, A. Turner, L. Ferrarese, H. Ford
The Hubble Spae Telesope Extragalati Distane Sale
Key Projet. 1: The disovery of Cepheids and a new distane to M81. Asand 5 oauthors.
trophysial Journal, Part 1, vol. 427, no. 2, pages 628655, 1994. (Cited on
page 62.)
[Funk
et al. 2008℄ S. Funk, O. Reimer, D. F. Torres and J. A. Hinton. The GeV-TeV
Connetion in Galati γ -ray soures. The Astrophysial Journal, vol. 679,
no. 2, pages 12991314, 2008. (Cited on pages 20, 22, 35, 67, 169 and 173.)
Searhing for Galati
Cosmi-Ray Pevatrons with Multi-TeV Gamma Rays and Neutrinos. The
[Gabii & Aharonian 2007℄ S. Gabii and F. A. Aharonian.
Astrophysial Journal, vol. 665, no. 2, pages L131L134, 2007.
pages 19, 22, 28, 35, 37, 40 and 45.)
(Cited on
154
[Gabii
Bibliography
et al. 2009℄ S. Gabii, F. A. Aharonian and S. Casanova. Broad-band nonthermal emission from moleular louds illuminated by osmi rays from
nearby supernova remnants. Monthly Noties of the Royal Astronomial
Soiety, vol. 396, no. 3, pages 16291639, 2009. (Cited on pages 19, 28, 54,
116, 117 and 176.)
Gamma Ray Astronomy and the Origin of Galati Cosmi
Rays. In XXI European Cosmi Ray Symposium. arXiv: astro-ph/0811.0836,
[Gabii 2008℄ S. Gabii.
2008. (Cited on page 122.)
[Gaensler
et al.
2006℄ B. M. Gaensler, S. Chatterjee, P. O. Slane, E. van der Swaluw,
The X-Ray Struture of the Pulsar Bow Shok
G189.22+2.90 in the Supernova Remnant IC 443. The Astrophysial JourF. Camilo and J. P. Hughes.
nal, vol. 648, no. 2, pages 10371042, 2006. (Cited on page 33.)
et al. 1995℄ T. K. Gaisser, F. Halzen and T. Stanev. Partile astrophysis
with high energy neutrinos [Erratum: 1996PhR...271..355G℄. Physis Re-
[Gaisser
ports, vol. 258, pages 173236, 1995. (Cited on page 55.)
et al. 1998℄ T. K. Gaisser, R. J. Protheroe and T. Stanev. Gamma-Ray
Prodution in Supernova Remnants. Astrophysial Journal, vol. 492, no. 1,
[Gaisser
pages 219227, 1998. (Cited on pages 19, 37 and 39.)
Observational Ponderings on Disk-Halo Interfaes. In Extra-Planar Gas, volume 331 of Astronomial Soiety of the Pai Conferene Series, pages 147154. R. Braun, 2005.
[Gallagher & Smith 2005℄ J. S. Gallagher and L. J. Smith.
(Cited on page 59.)
Calibration of the MAGIC telesope and Observation of
Gamma Ray Bursts. PhD thesis, Univ. Autonoma de Barelona, 2006. (Cited
[Gaug 2006℄ M. Gaug.
on page 94.)
[Ginzburg & Syrovatskii 1964℄ V. L. Ginzburg and S. I. Syrovatskii. The origin of
osmi rays.
New York: Mamillan, 1964.
(Cited on pages 2, 21, 35, 59
and 61.)
[Green 2004℄ D. A. Green.
some statistis.
Galati supernova remnants: an updated atalogue and
Bulletin of the Astronomial Soiety of India, vol. 32, pages
335370, 2004. (Cited on page 31.)
[Halzen & Klein 2010℄ F. Halzen and S. R. Klein.
An instrument for neutrino astronomy.
Invited Review Artile: IeCube:
Review of Sienti Instruments,
vol. 81, no. 8, pages 081101+, 2010. (Cited on page 14.)
Astropartile physis with high energy neutrinos: from
AMANDA to IeCube. The European Physial Journal C, vol. 46, no. 3,
[Halzen 2006℄ F. Halzen.
pages 669687, 2006. (Cited on page 54.)
Bibliography
[Hartman
et al.
155
1999℄ R.C. Hartman, D. L. Bertsh, S. D. Bloom, A. W. Chen,
P. Deines-Jones, J. A. Esposito, C. E. Fihtel, D. P. Friedlander, S. D.
Hunter, L. M. MDonald and 17 oauthors.
of High-Energy Gamma-Ray Soures.
The Third EGRET Catalog
Astrophysial Journal Supplement Se-
ries, vol. 123, no. 1, pages 79202, 1999. (Cited on pages 5, 12, 34, 43, 103,
110 and 175.)
[Hek
et al.
1998℄ D. Hek, J. Knapp, J. N. Capdevielle, G. Shatz and T. Thouw.
Forshungszentrum
Karlsruhe,
Hannover
(Germany),
1998.
(Cited
on
page 93.)
[Hermsen 1990℄ W. Hermsen.
Highlights from the COS-B mission.
Advanes in
Spae Researh, vol. 10, pages 6979, 1990. (Cited on page 4.)
Uber Beobahtungen der durhdringenden Strahlung bei sieben
Freiballonfahrten. Physikalishe Zeitshrift, vol. 13, pages 10841091, 1912.
[Hess 1912℄ V. Hess.
(Cited on page 1.)
[Hewitt
et al.
2006℄ J. W. Hewitt, F. Yusef-Zadeh, M. Wardle, D. A. Roberts and
Green Bank Telesope Observations of IC 443: The Nature
of OH (1720 MHz) Masers and OH Absorption. The Astrophysial Journal,
N. E. Kassim.
vol. 652, no. 2, pages 12881296, 2006. (Cited on page 31.)
[Hillas 1985℄ A.M. Hillas.
gamma.
Cerenkov light images of EAS produed by primary
In F. C. Jones, editeur, International Cosmi Ray Conferene, vol-
ume 3, pages 445448, 1985. (Cited on page 94.)
et al. 2010℄ W. Hofmann, M. Martinez and the CTA onsortium. Design
Conepts for the Cherenkov Telesope Array. eprint arXiv:1008.3703v2, 2010.
[Hofmann
(Cited on page 111.)
[Holder
et al.
2005℄ J. Holder, H. M. Badran, G. Blaylok, I. H. Bond, P. J. Boyle,
S. M. Bradbury, J. H. Bukley, K. Byrum, D. A. Carter-Lewis, O. Celik
and 63 oauthors.
sope.
Reent Observations of IC443 with the Whipple 10m Telend International Sympo-
In High Energy Gamma-Ray Astronomy: 2
sium. Heidelberg (Germany), volume 745 of
AIP Conferene Proeedings,
pages 275280. New York: Amerian Institute of Physis, 2005. (Cited on
page 34.)
[Huang
et al. 1986℄ Y.-L. Huang, R. L. Dikman and R. L. Snell. IRAS soures
assoiated with shoked gas regions in IC 443. Astrophysial Journal, Part 2
- Letters to the Editor, vol. 302, pages L63L66, 1986. (Cited on pages 34,
127 and 177.)
et al. 1994℄ D.H. Hughes, W.K. Gear and E.I. Robson. The Submillimetre Struture of the Starburst Nuleus in M82 - a Diration-Limited 450MICRON Map. Monthly Noties of the Royal Astronomial Soiety, vol. 270,
[Hughes
no. 3, page 641, 1994. (Cited on pages 66 and 173.)
156
Bibliography
[Humensky & the VERITAS Collaboration 2008℄ T. B. Humensky and the VERITAS Collaboration.
Observation of the Supernova Remnant IC 443 with
VERITAS. In Pro. of the 30th International Cosmi Ray Conferene.Mérida,
Yuatán, Mexio, volume 2, pages 835838. Universidad Naional Autónoma
de Méxio, Mexio City, Mexio, 2008. (Cited on page 34.)
[Issa & Wolfendale 1981℄ M. R. Issa and A. W. Wolfendale.
osmi ray irradiation of loal moleular louds.
Gamma rays from the
Nature, vol. 292, pages
430433, 1981. (Cited on page 122.)
et al. 2005℄ T. Kamae, T. Abe and T. Koi. Dirative Interation and
Saling Violation in pp>π 0 Interation and GeV Exess in Galati Diuse
Gamma-Ray Spetrum of EGRET. The Astrophysial Journal, vol. 620,
[Kamae
no. 1, pages 244256, 2005. (Cited on page 51.)
[Karahentsev
et al.
2003℄ I. D. Karahentsev, E. K. Grebel, M. E. Sharina, A. E.
Dolphin, D. Geisler, P. Guhathakurta, P. W. Hodge, V. E. Karahentseva,
A. Sarajedini and P. Seitzer.
Distanes to nearby galaxies in Sulptor.
As-
tronomy and Astrophysis, vol. 404, pages 93111, 2003. (Cited on page 74.)
[Kelner
et al. 2006℄ S. R. Kelner, F. A. Aharonian and V. V. Bugayov. Energy
spetra of gamma rays, eletrons, and neutrinos produed at proton-proton
interations in the very high energy regime. Physial Review D, vol. 74, no. 3,
page 034018, 2006. (Cited on pages 20, 52, 53, 54, 59 and 172.)
[Keohane
et al.
1997℄ J. W. Keohane, R. Petre, E. V. Gotthelf, M. Ozaki and
A Possible Site of Cosmi Ray Aeleration in the Supernova
Remnant IC 443. Astrophysial Journal, vol. 484, pages 350359, 1997.
K. Koyama.
(Cited on page 33.)
Reherhe de soures gamma par un methode de Maximum
de Vraisemblane: Appliation aux AGN et aux soures galatiques suivis par
le telesope CAT. PhD thesis, University of Caen, Frane, 2003. (Cited on
[Kheli 2003℄ B. Kheli.
page 34.)
[Klein
et al. 1988℄ U. Klein, R. Wielebinski and H.W. Morsi. Radio ontinuum observations of M82. Astronomy and Astrophysis, vol. 190, no. 1, pages 4146,
1988. (Cited on pages 66 and 173.)
Disovery of new variable radio soures in the nuleus of the nearby galaxy Messier 82. Siene,
[Kronberg & Sramek 1985℄ P.P. Kronberg and R.A. Sramek.
vol. 227, pages 2831, 1985. (Cited on page 66.)
[Kronberg & Wilkinson 1975℄ P. P. Kronberg and P. N. Wilkinson.
multifrequeny radio observations of M82.
High-resolution,
Astrophysial Journal, vol. 200,
no. 1, pages 430438, 1975. (Cited on page 66.)
Bibliography
157
et al. 1985℄ P.P. Kronberg, P. Biermann and F.R. Shwab. The nuleus
of M82 at radio and X-ray bands - Disovery of a new radio population of
supernova andidates. Astrophysial Journal, vol. 291, no. 1, pages 693707,
[Kronberg
1985. (Cited on page 66.)
[Lamb & Maomb 1997℄ R. C. Lamb and D. J. Maomb.
Gamma Rays.
Point Soures of GeV
Astrophysial Journal, vol. 488, pages 872880, 1997. (Cited
on pages 34 and 43.)
et al. 1990℄ T.L. Landeker, M. Clutton-Brok and C.R. Purton. G
65.1+0.6 - A new supernova remnant of low surfae brightness. Astronomy
[Landeker
and Astrophysis, vol. 232, no. 1, pages 207214, 1990. (Cited on pages 102,
105 and 175.)
[Lasker
et al.
1990℄ B. M. Lasker, C. R. Sturh, B. J. MLean, J. L. Russell,
The Guide Star Catalog. I - Astronomial foundations and image proessing. Astronomial Journal, vol. 99, pages
H. Jenkner and M. M. Shara.
20192058, 1990. (Cited on pages 31, 32, 34 and 170.)
1420 and 408 MHz Continuum Observations of the IC
443/G189.6+3.3 Region. The Astronomial Journal, vol. 127, no. 4, pages
[Leahy 2004℄ A. D. Leahy.
22772283, 2004. (Cited on page 31.)
et al. 2001℄ R. W. Lessard, J. H. Bukley, V. Connaughton and S. Le Bohe. A new analysis method for reonstruting the arrival diretion of TeV
gamma rays using a single imaging atmospheri Cherenkov telesope. As-
[Lessard
tropartile Physis, vol. 15, no. 1, pages 118, 2001. (Cited on page 99.)
[Lindner 2003℄ J. Lindner.
Dusty galaxies: modelling spetral energy distributions.
Canadian Undergraduate Physis Journal, vol. 2, no. 1, pages 712, 2003.
(Cited on page 69.)
[Lipari 1993℄ P. Lipari.
Tev muons in hadroni showers.
Astropartile Physis,
vol. 1, no. 4, pages 399415, 1993. (Cited on page 55.)
The umulative bakground of
high energy neutrinos from starburst galaxies. Journal of Cosmology and
[Loeb & Waxman 2006℄ A. Loeb and E. Waxman.
Astropartile Physis, vol. 5, no. 003, pages 28, 2006. (Cited on pages 57
and 72.)
[Longair 1992℄ M. S. Longair. volume 1. Cambridge University Press, Cambridge,
UK, 1992. (Cited on page 83.)
[Longair 1994℄ M. S. Longair.
volume 2.
Cambridge University Press,
2nd
ed.,
Cambridge, UK, 1994. (Cited on page 61.)
The radio brightness-diameter relation for supernova remnants - Some new distane alibrators. Soviet Astronomy Letters,
[Lozinskaya 1981℄ T. A. Lozinskaya.
vol. 7, pages 1719, 1981. (Cited on page 33.)
158
Bibliography
MAGIC gamma-ray observations of distant
AGN and a study of soure variability and the extragalati bakground light
using Fermi and air Cherenkov telesopes. PhD thesis, University of Udine,
[Mankuzhiyil 2010℄ Nijil Mankuzhiyil.
2010. (Cited on pages 95 and 174.)
[Mannheim & Shlikeiser 1994℄ K. Mannheim and R. Shlikeiser.
osmi ray nulei.
Interations of
Astronomy & Astrophysis, vol. 286, pages 983996, 1994.
(Cited on page 61.)
et al. 1968℄ L. Marashi, G. C. Perola and S. Shwarz. X-ray ux and
anisotropy produed by galati osmi-ray eletrons. Il Nuovo Cimento B
[Marashi
Series 10, vol. 53, no. 2, pages 443458, 1968. (Cited on page 59.)
MAGIC onrms VHE gamma-ray emission from
HESS J0632+057 between 7-9 Feb 2011. The Astronomer's Telegram,
[Mariotti 2011℄ M. Mariotti.
vol. 3161, pages 1+, 2011. (Cited on page 10.)
et al. 1999℄ S. Marko, F. Melia and I. Sarevi. High-Energy Emission
from Relativisti Partiles in Sagittarius A*. The Astrophysial Journal,
[Marko
vol. 522, no. 2, pages 870878, 1999. (Cited on page 59.)
Energeti seondary
eletrons and the nonthermal galati radio bakground - A probe of the magneti eld in interstellar louds. Astrophysial Journal, vol. 221, no. 1, pages
[Marsher & Brown 1978℄ A. P. Marsher and R. L. Brown.
588597, 1978. (Cited on page 59.)
[Mauersberger
et al.
1996℄ R. Mauersberger, C. Henkel, R. Wielebinski, T. Wiklind
and H.-P. Reuter.
I. NGC 253.
Moleular distribution and kinematis in nearby galaxies.
Astronomy and Astrophysis, vol. 305, pages 421434, 1996.
(Cited on page 74.)
et al. 2005℄ Y. D. Mayya, L. Carraso and A. Luna. The Disovery of Spiral
Arms in the Starburst Galaxy M82. The Astrophysial Journal, vol. 628,
[Mayya
no. 1, pages L33L36, 2005. (Cited on page 62.)
[Mayya
et al.
2006℄ Y. D. Mayya, A. Bressan, L. Carraso and L. Hernandez-
Martinez.
M82.
The Star Formation History of the Disk of the Starburst Galaxy
The Astrophysial Journal, vol. 649, no. 1, pages 172180, 2006. (Cited
on page 63.)
A study of very high energy gamma-ray emission from
AGNs and onstraints on the extragalati bakground light. PhD thesis,
[Mazin 2007℄ D. Mazin.
Tehnishe Universität Münhen, 2007. (Cited on pages 92 and 174.)
et al. 1993℄ K. K. MLeod, G. H. Rieke, M. J. Rieke and D. M. Kelly. M82
- The saga ontinues. Astrophysial Journal, vol. 412, no. 1, pages 111126,
[MLeod
1993. (Cited on page 66.)
Bibliography
[Melo
et al.
159
2002℄ V. P. Melo, A. M. Pérez Garía, J. A. Aosta-Pulido, C. Muñoz
Tuñón and J. M. Rodríguez Espinosa.
Infrared Emission in NGC 253.
The Spatial Distribution of the Far-
The Astrophysial Journal, vol. 574, no. 2,
pages 709718, 2002. (Cited on page 74.)
[Meui
et al.
2007℄ M. Meui, R. Paoletti, R. Pegna, A. N. Stamerra Turini,
D. Corti, M. Mariotti and the MAGIC Collaboration. The trigger system of
the MAGIC telesope: on-line seletion strategies for Cherenkov telesopes.
IEEE Trans. Nul. Si., vol. 54, no. 2, pages 404409, 2007.
(Cited on
pages 90 and 174.)
et al.
[Moiseev
2007℄ A. A. Moiseev, R. C. Hartman, J. F. Ormes, D. J. Thomp-
son, M. J. Amato, T. E. Johnson, K. N. Segal and D. A. Sheppard.
anti-oinidene detetor for the GLAST large area telesope.
The
Astropartile
Physis, vol. 27, no. 5, pages 339358, 2007. (Cited on page 20.)
On gamma-ray soures, supernova remnants, OB
assoiations, and the origin of osmi rays. Astrophysial Journal, vol. 231,
[Montmerle 1979℄ T. Montmerle.
no. 1, pages 95110, 1979. (Cited on page 19.)
[Moralejo
et al.
2009℄ A. Moralejo, M. Gaug, E. Carmona, P. Colin, C. Delgado,
S. Lombardi, D. Mazin, V. Salzotto, J. Sitarek, D. Tesaro and for the
MARS, the MAGIC Analysis and Reonstrution
Software. In Pro. 31st International Cosmi Ray Conferene (Šód¹, Poland).
MAGIC ollaboration.
arXiv: astro-ph/0907.0943, 2009. (Cited on pages 93, 104 and 130.)
[Moskalenko & Strong 1998℄ I. Moskalenko and A. Strong.
tion of Cosmi-Ray Positrons and Eletrons.
Prodution and Propaga-
Astrophysial Journal, vol. 493,
pages 694715, 1998. (Cited on page 59.)
[Mouhine
et al.
2005℄ M. Mouhine, H. C. Ferguson, R. M. Rih, T. M. Brown and
T. E. Smith. Halos of Spiral Galaxies. I. The Tip of the Red Giant Branh
as a Distane Indiator. The Astrophysial Journal, vol. 633, no. 2, pages
810820, 2005. (Cited on page 74.)
[Mufson
et al.
1986℄ S. L. Mufson, M. L. MCollough, J. R. Dikel, R. Petre,
R. White and R. Chevalier.
nova remnant IC 443.
A multiwavelength investigation of the super-
Astronomial Journal, vol. 92, pages 13491357, 1986.
(Cited on page 33.)
[Naito & Takahara 1994℄ T. Naito and F. Takahara.
sion from supernova remnants.
High energy gamma-ray emis-
Journal of Physis G: Nulear and Partile
Physis, vol. 20, no. 3, pages 477486, 1994. (Cited on page 19.)
[Nolan
et al. 2003℄ P. L. Nolan, W. F. Tompkins, I. A. Grenier and P. F. Mihelson.
Variability of EGRET Gamma-Ray Soures. The Astrophysial Journal
vol. 597, no. 1, pages 615627, 2003. (Cited on page 34.)
160
Bibliography
[O'Connell & Mangano 1978℄ R. W. O'Connell and J. J. Mangano.
regions of M82.
The entral
Astrophysial Journal, vol. 221, no. 1, pages 6279, 1978.
(Cited on page 62.)
[Ohm
et al. 2009℄ S. Ohm, C. van Eldik and K. Egberts. γ /hadron separation in
very-high-energy γ -ray astronomy using a multivariate analysis method. Astropartile Physis, vol. 31, no. 5, pages 383391, 2009. (Cited on page 120.)
[Olbert
et al.
2001℄ C. M. Olbert, C. R. Cleareld, N. E. Williams, J. W. Keohane
and D. A. Frail. A Bow Shok Nebula around a Compat X-Ray Soure in
the Supernova Remnant IC 443. Astrophysial Journal, vol. 554, no. 2, pages
L205L208, 2001. (Cited on pages 33, 39, 43 and 125.)
VERITAS Reports Inreased Ativity of HESS J0632+057
in Very High Energy Gamma Rays. The Astronomer's Telegram, vol. 3153,
[Ong 2011℄ R. A. Ong.
pages 1+, 2011. (Cited on page 10.)
[Ormes
et al. 1988℄ J. F. Ormes, M. E. Ozel and D. J. Morris. On the high-energy
gamma-ray signature of osmi-ray soures. The Astrophysial Journal,
vol. 334, pages 722733, 1988. (Cited on pages 25 and 37.)
Seondary osmi-ray eletrons and positrons from 1 to 100 GeV in the upper atmosphere and interstellar spae, and interpretation of a reent positron ux measurement. As-
[Orth & Bungton 1976℄ C. D. Orth and A. Bungton.
trophysial Journal, vol. 206, no. 1, pages 312332, 1976. (Cited on page 59.)
[Ott
et al. 2005℄ J. Ott, A. Weiÿ, C. Henkel and F. Walter. The Temperature Distribution of Dense Moleular Gas in the Center of NGC 253. The Astrophysial
Journal, vol. 629, no. 2, pages 767780, 2005. (Cited on pages 77 and 174.)
[Oya 2010℄ I. Oya.
sope.
[Paglione
Observations of Ative Galati Nulei with the MAGIC Tele-
PhD thesis, Univ. Complutense de Madrid, 2010. (Cited on page 94.)
et al.
Bertsh.
1996℄ T. A. D. Paglione, A. P. Marsher, J. M. Jakson and D. L.
Diuse Gamma-Ray Emission from the Starburst Galaxy NGC 253.
Astrophysial Journal, vol. 460, pages 295302, 1996.
(Cited on pages 57,
59, 63 and 74.)
[Pavlidou & Fields 2001℄ V. Pavlidou and B. Fields.
Loal Group Galaxies.
Diuse Gamma Rays from
The Astrophysial Journal, vol. 558, no. 1, pages
6371, 2001. (Cited on page 63.)
[Persi
et al. 2008℄
from M 82.
M. Persi, Y. Rephaeli and Y. Arieli.
Very-high-energy emission
Astronomy and Astrophysis, vol. 486, no. 1, pages 143149,
2008. (Cited on pages 57, 63, 64 and 69.)
[Punh
et al.
1992℄ M. Punh, C. W. Akerlof, M. F. Cawley, M. Chantell, D. J.
Fegan, S. Fennell, J. A. Gaidos, J. Hagan, A. M. Hillas, Y. Jiang, A. D.
Bibliography
161
Kerrik, R. C. Lamb, M. A. Lawrene, D. A. Lewis, D. I. Meyer, G. Mohanty, K. S. O'Flaherty, P. T. Reynolds, A. C. Rovero, M. S. Shubnell,
G. Sembroski, T. C. Weekes and C. Wilson.
the ative galaxy Markarian 421.
Detetion of TeV photons from
Nature, vol. 358, no. 6386, pages 477478,
1992. (Cited on page 7.)
[Ramaty & Lingenfelter 1966℄ R. Ramaty and R. E. Lingenfelter.
Ray Eletrons.
Galati Cosmi-
Journal of Geophysial Researh, vol. 71, pages 3687+, 1966.
(Cited on page 59.)
et al. 2008℄ P. Ranalli, A. Comastri, L. Origlia and R. Maiolino. A deep
X-ray observation of M82 with XMM-Newton. Monthly Noties of the Royal
[Ranalli
Astronomial Soiety, vol. 386, no. 3, pages 14641480, 2008.
(Cited on
page 62.)
[Reimer 2001℄ O. Reimer.
Gamma-Ray Properties of Unidentied EGRET Soures.
In The Nature of Unidentied Galati High-Energy Gamma-Ray Soures.
Tonantzintla, Puebla, Mexio, volume 267 of
Library,
Astrophysis and Spae Siene
pages 1734. Kluwer Aademi Publishers Dordreht, 2001. (Cited
on page 40.)
[Rekola
et al.
2005℄ R. Rekola, M. G. Riher, Marshall L. MCall, M. J. Valtonen,
J. K. Kotilainen and Chris Flynn.
tary nebula luminosity funtion.
Distane to NGC 253 based on the plane-
Monthly Noties of the Royal Astronomial
Soiety, vol. 361, no. 1, pages 330336, 2005. (Cited on page 74.)
[Rho
et al. 2001℄ J. Rho, T. H. Jarrett, R. M. Cutri and W. T. Reah. Near-Infrared
Imaging and [O I℄ Spetrosopy of IC 443 using Two Miron All Sky Survey
and Infrared Spae Observatory. The Astrophysial Journa, vol. 547, no. 2,
pages 885898, 2001. (Cited on page 31.)
[Rie
et al.
1988℄ W. Rie, C. J. Lonsdale, B. T. Soifer, G. Neugebauer, E. L. Kopan,
Lawrene A. Lloyd, T. de Jong and H. J. Habing.
vations of large optial galaxies.
A atalog of IRAS obser-
Astrophysial Journal Supplement Series,
vol. 68, pages 91127, 1988. (Cited on page 74.)
[Rieke
et al. 1973℄ G. H. Rieke, D. A. Harper, F. J. Low and K. R. Armstrong.
350-MICRON Observations of Soures in H II Regions, the Galati Center,
and NGC 253. Astrophysial Journal, vol. 183, pages L67L71, 1973. (Cited
on pages 77 and 174.)
[Rieke
et al.
1980℄ G. H. Rieke, M. J. Lebofsky, R. I. Thompson, F. J. Low and
A. T. Tokunaga.
The nature of the nulear soures in M82 and NGC 253.
Astrophysial Journal, vol. 238, no. 1, pages 2440, 1980. (Cited on page 66.)
[Rodríguez Marrero
et al.
2008℄ A.
Y.
Rodríguez
Marrero,
E. de Cea del Pozo, O. Reimer and A. N. Cillis.
D.
F.
Torres,
Diusion of Cosmi
162
Bibliography
Rays and the Gamma-Ray Large Area Telesope: Phenomenology at the
1-100 GeV Regime. The Astrophysial Journal, vol. 689, no. 1, pages
213218, 2008. (Cited on pages 16, 19 and 20.)
[Rodríguez Marrero
et al.
2009℄ A.
E. de Cea del Pozo.
Y.
Rodríguez
Marrero,
D.
F.
Torres
and
The GeV to TeV view of SNR IC443: preditions for
Fermi. In 6th Workshop on Siene with the New Generation of High Energy
Gamma-Ray Experiments (SiNeGHE '08). arXiv:
astro-ph/0901.2615v1,
2009. (Cited on pages 16, 28, 38, 45, 48, 116 and 171.)
[Rolke
et al. 2005℄ W. A. Rolke, A. M. López and J. Conrad. Limits and ondene
intervals in the presene of nuisane parameters. Nulear Instruments and
Methods in Physis Researh Setion A, vol. 551, no. 2-3, pages 493503,
2005. (Cited on page 106.)
et al. 1999℄ G. E. Romero, P. Benaglia and D. F. Torres. Unidentied 3EG
gamma-ray soures at low galati latitudes. Astronomy and Astrophysis,
[Romero
vol. 348, pages 868876, 1999. (Cited on page 40.)
et al. 2007℄ M. Rosado, L. Arias and P. Ambroio-Cruz. Kinematis of the
Moleular Hydrogen Assoiated with the Supernova Remnant IC 443. The
[Rosado
Astronomial Journal, vol. 133, no. 1, pages 8998, 2007. (Cited on pages 33,
34 and 50.)
[Sabatini
et al.
2010℄ S. Sabatini, M. Tavani, E. Striani, A. Bulgarelli, V. Vittorini,
G. Piano, E. Del Monte, M. Feroi, F. de Pasquale, M. Trifoglio and 51
Episodi Transient Gamma-ray Emission from the Miroquasar
Cygnus X-1. The Astrophysial Journal Letters, vol. 712, pages L10L15,
oauthor.
2010. (Cited on page 10.)
Detetion of the Red Giant
Branh Stars in M82 Using the Hubble Spae Telesope. The Astrophysial
[Sakai & Madore 1999℄ S. Sakai and B. F. Madore.
Journal, vol. 526, no. 2, pages 599606, 1999. (Cited on page 62.)
[Saz Parkinson
et al.
2010℄ P.M. Saz Parkinson, M. Dormody, M. Ziegler, P. S. Ray,
A. A. Abdo, J. Ballet, M. G. Baring, A. Belore, T. H. Burnett, G. A.
Eight -ray Pulsars Disovered in Blind Frequeny Searhes of Fermi LAT Data. Astrophysial Journal, vol. 725, no. 1,
Caliandro and 27 oauthors.
pages 571584, 2010. (Cited on pages 109, 110 and 175.)
[Seiradakis
et al.
H. Kühr.
1985℄ J. H. Seiradakis, W. Reih, W. Sieber, R. Shlikeiser and
An extended extragalati radio soure behind the Milky Way.
As-
tronomy and Astrophysis, vol. 143, no. 2, pages 478480, 1985. (Cited on
page 103.)
[Seta
et al.
1998℄ M. Seta,
T. Hasegawa,
T. M. Dame,
S. Sakamoto,
T. Handa, M. Hayashi, J.-I. Morino, K. Sorai and K. S. Usuda.
T. Oka,
Enhaned
Bibliography
163
CO J=(2-1)/J=(1-0) Ratio as a Marker of Supernova Remnant − Moleular Cloud Interations: The Cases of W44 and IC 443. The Astrophysial
Journal, vol. 505, no. 1, pages 286298, 1998. (Cited on pages 33 and 44.)
[Smith
et al.
1991℄ P. A. Smith, P. W. J. L. Brand, C. M. Mountain, P. J. Puxley
and N. Nakai.
The (C-12)O to H2 ratio in the entre of M82.
Monthly
Noties of the Royal Astronomial Soiety, vol. 252, pages 6P11P, 1991.
(Cited on page 63.)
The Cosmi γ -Ray Spetrum from Seondary Partile
Prodution in Cosmi-Ray Interations. Astrophysis and Spae Siene,
[Steker 1970℄ F. W. Steker.
vol. 6, no. 3, pages 377389, 1970. (Cited on page 59.)
Observations of galati gamma-rays and their impliations for galati struture studies. Astrophysial Journal, vol. 212, no. 1,
[Steker 1977℄ F. W. Steker.
pages 6070, 1977. (Cited on page 59.)
Upper Limits to Fluxes of Neutrinos and Gamma-Rays
from Starburst Galaxies. Journal of Physis: Conferene Series, vol. 60, no. 1,
[Steker 2007℄ F. W. Steker.
pages 215218, 2007. (Cited on pages 57 and 73.)
Prodution spetrum of gamma rays in interstellar spae through neutral pion deay. Astro-
[Stephens & Badhwar 1981℄ S. A. Stephens and G. D. Badhwar.
physis and Spae Siene, vol. 76, no. 1, pages 213233, 1981.
(Cited on
page 51.)
et al. 1997℄ D. K. Strikland, T. J. Ponman and I. R. Stevens. ROSAT
observations of the galati wind in M 82. Astronomy and Astrophysis,
[Strikland
vol. 320, pages 378394, 1997. (Cited on page 62.)
[Strong & Moskalenko 1998℄ A. Strong and I. Moskalenko.
Ray Nuleons in the Galaxy.
Propagation of Cosmi-
The Astrophysial Journal, vol. 509, no. 1,
pages 212228, 1998. (Cited on page 59.)
et al. 1997℄ S. J. Sturner, J. G. Skibo, C. D. Dermer and J. R. Mattox.
Temporal Evolution of Nonthermal Spetra from Supernova Remnants. As-
[Sturner
trophysial Journal, vol. 490, no. 2, pages 619632, 1997. (Cited on page 19.)
[Swanenburg
et al.
1981℄ B.N. Swanenburg, K. Bennett, G. F. Bignami, R. Bu-
heri, P. Caraveo, W. Hermsen, G. Kanbah, G. G. Lihti, J. L. Masnou,
H. A. Mayer-Hasselwander and 4 oauthors.
energy gamma-ray soures.
Seond COS B atalog of high-
Astrophysial Journal, Part 2 - Letters to the
Editor, vol. 243, pages L69L73, 1981. (Cited on page 103.)
[Tabatabaei
et al.
1
4
2007℄ F. S. Tabatabaei, R. Bek, E. Kr gel, M. Krause, E. M.
High-resolution radio ontinuum survey of M 33. II. Thermal and nonthermal emission. Astronomy
Berkhuijsen, K. D. Gordon and K. M. Menten.
and Astrophysis, vol. 475, no. 1, pages 133143, 2007. (Cited on page 68.)
164
Bibliography
[Tamm & Frank 1937℄ I. E. Tamm and I. M. Frank.
eletrons in a medium.
Coherent radiation of fast
Doklady Akademii Nauk SSSR, vol. 14, page 107,
1937. (Cited on page 84.)
[Tanaka & Takahara 2009℄ S. J. Tanaka and F. Takahara.
Evolution of Pulsar Wind
A Model of the Spetral
Nebulae. In Pro. 1st Fermi Symposium (Wash-
ington, DC). arXiv: astro-ph/1001.2360, 2009. (Cited on page 110.)
Evidene for Nonlinear
Diusive Shok Aeleration of Cosmi Rays in the 2006 Outburst of the
Reurrent Nova RS Ophiuhi. The Astrophysial Journal, vol. 663, pages
[Tatishe & Hernanz 2007℄ V. Tatishe and M. Hernanz.
L101L104, 2007. (Cited on page 10.)
Evidene for Nonlinear
Diusive Shok Aeleration of Cosmi Rays in the 2006 Outburst of RS
Ophiuhi. In RS Ophiuhi (2006) and the Reurrent Nova Phenomenon,
volume 401 of Astronomial Soiety of the Pai Conferene Series, pages
[Tatishe & Hernanz 2008℄ V. Tatishe and M. Hernanz.
328+. A. Evans, M. F. Bode, T. J. O'Brien, & M. J. Darnley, 2008. (Cited
on page 10.)
et al.
[Tavani
2010℄ M. Tavani, A. Giuliani, A. W. Chen, A. Argan, G. Barbi-
ellini, A. Bulgarelli, P. Caraveo, P. W. Cattaneo, V. Coo, T. Contessi
Diret Evidene for Hadroni Cosmi-Ray Aeleration
in the Supernova Remnant IC 443. Astrophysial Journal Letters, vol. 710,
and 52 oauthors.
no. 2, pages L151L155, 2010. (Cited on page 42.)
[Teleso & Harper 1980℄ C. M. Teleso and D. A. Harper.
emission.
Galaxies and far-infrared
Astrophysial Journal, vol. 235, no. 1, pages 392404, 1980. (Cited
on pages 69, 74, 77 and 174.)
et al. 1991℄ C. M. Teleso, M. Joy, K. Dietz, R. Deher and H. Campins.
Infrared mapping of M82 - A starburst in an edge-on barred galaxy. Astro-
[Teleso
physial Journal, vol. 369, no. 1, pages 135146, 1991. (Cited on page 62.)
[Tesaro
et al.
2007℄ D.
Tesaro,
H.
Bartko,
N.
Galante,
F.
Göbel
and
the
MAGIC Collaboration. Study of the performane and apability of the new
ultra-fast 2 GSample/s FADC data aquisition system of the MAGIC telesope. ArXiv: astro-ph/0709.1410, 2007. (Cited on page 96.)
TeV gamma-ray observations of nearby Ative Galati
Nulei with the MAGIC telesope: exploring the high energy region of the
multiwavelength piture. PhD thesis, Univ. Autonoma de Barelona, 2010.
[Tesaro 2010℄ D. Tesaro.
(Cited on pages 87 and 174.)
[Tian & Leahy 2006℄ W.W. Tian and D.A. Leahy.
G65.1+0.6 And The PSR J1957+2831.
Assoiation Of The SNR
Bulletin of the Amerian Astro-
nomial Soiety, vol. 455, page 1053, 2006. (Cited on pages 102 and 103.)
Bibliography
165
[Torres & Domingo-Santamaría 2005℄ D. F. Torres and E. Domingo-Santamaría.
Some Comments on the High Energy Emission from Regions of Star Formation Beyond the Galaxy. Modern Physis Letters A, vol. 20, no. 37, pages
28272843, 2005. (Cited on pages 60 and 173.)
[Torres
et al.
2001a℄ D. F. Torres, G. E. Romero, J. A. Combi, P. Benaglia, H. An-
dernah and B. Punsly.
gamma-ray soures.
A variability analysis of low-latitude unidentied
Astronomy and Astrophysis, vol. 370, pages 468478,
2001. (Cited on page 34.)
[Torres
et al. 2001b℄ D. R. Torres, M. E. Pessah and G. E. Romero. On the time
variability of Gamma-ray soures: a numerial analysis of variability indies.
Astronomishe Nahrihten, vol. 322, no. 4, pages 223227, 2001. (Cited on
page 40.)
[Torres
et al.
2003℄ D. F. Torres, Gustavo E. Romero, T. M. Dame, J. A. Combi
and Y. M. Butt.
Supernova remnants and γ−ray soures.
Physis Reports,
vol. 382, no. 6, pages 303380, 2003. (Cited on pages 31, 32, 33, 40, 44, 128
and 170.)
[Torres
et al.
2004℄ D. F. Torres, O. Reimer, E. Domingo-Santamaría and S. W.
Digel. Luminous Infrared Galaxies as Plausible Gamma-Ray Soures for
the Gamma-Ray Large Area Spae Telesope and the Imaging Atmospheri
Cerenkov Telesopes. The Astrophysial Journal, vol. 607, no. 2, pages L99
L102, 2004. (Cited on pages 57, 63 and 69.)
[Torres
et al. 2008℄ D. F. Torres, A. Y. Rodríguez Marrero and E. de Cea del Pozo.
MAGIC J0616+225 as delayed TeV emission of osmi rays diusing from
the supernova remnant IC 443. Monthly Noties of the Royal Astronomial
Soiety: Letters, vol. 387, no. 1, pages L59L63, 2008. (Cited on pages 16,
22, 25, 31, 35, 128 and 129.)
[Torres
et al. 2010℄ D. F. Torres, A.Y. Rodríguez Marrero and E. de Cea Del Pozo.
The GeV to TeV onnetion in the environment of SNR IC 443. Monthly
Noties of the Royal Astronomial Soiety, vol. 408, no. 2, pages 12571266,
2010. (Cited on pages 16, 41, 49 and 172.)
Theoretial Modeling of the Diuse Emission of Gamma
Rays from Extreme Regions of Star Formation: The Case of ARP 220.
[Torres 2004℄ D. F. Torres.
The Astrophysial Journal, vol. 617, no. 2, pages 966986, 2004.
(Cited
on pages 45, 57, 58, 63 and 68.)
[Troja
et al. 2006℄ E. Troja, F. Bohino and F. Reale. XMM-Newton Observations
of the Supernova Remnant IC 443. I. Soft X-Ray Emission from Shoked
Interstellar Medium. The Astrophysial Journal, vol. 649, no. 1, pages 258
267, 2006. (Cited on pages 33 and 34.)
166
Bibliography
[Turner & Ho 1985℄ J. L. Turner and P. T. P. Ho.
possible nulear ejetion in NGC 253.
The 1 parse radio ore and
Astrophysial Journal, vol. 299, no. 2,
pages L77L81, 1985. (Cited on page 74.)
[Völk
et al. 1989℄ H. J. Völk, U. Klein and R. Wielebinski. M82, the Galaxy, and
the dependene of osmi ray energy prodution on the supernova rate. Astronomy and Astrophysis, vol. 213, no. 1, pages L12L14, 1989. (Cited on
page 68.)
[Völk
et al. 1996℄ H. J. Völk, F. A. Aharonian and D. Breitshwerdt. The Nonthermal Energy Content and Gamma-Ray Emission of Starburst Galaxies and
Clusters of Galaxies. Spae Siene Reviews, vol. 75, no. 1, pages 279297,
1996. (Cited on pages 63 and 64.)
[Volkova 1980℄ L. V. Volkova.
spheri Neutrinos.
Energy Spetra and Angular Distributions of Atmo-
Sov. J. Nul. Phys., vol. 31, pages 784, 1980. (Cited on
page 55.)
[Wang
et al. 1992℄ Z. R. Wang, I. Asaoka, S. Hayakawa and K. Koyama. Hard Xrays from the supernova remnant IC 443. Astronomial Soiety of Japan,
Publiations, vol. 44, no. 3, pages 303308, 1992. (Cited on page 33.)
[Waxman & Bahall 1999℄ E. Waxman and J. Bahall.
astrophysial soures: An upper bound.
High energy neutrinos from
Physial Review D, vol. 59, no. 2,
pages 023002+, 1999. (Cited on page 73.)
[Weaver
et al.
2002℄ K.
A.
Weaver,
T.
M.
Hekman,
D.
K.
Strikland
and
Chandra Observations of the Evolving Core of the Starburst
Galaxy NGC 253. The Astrophysial Journal, vol. 576, no. 1, pages L19
M. Dahlem.
L23, 2002. (Cited on page 72.)
[Weekes
et al.
1989℄ T. C. Weekes, M. F. Cawley, D. J. Fegan, K. G. Gibbs, A. M.
Hillas, P. W. Kowk, R. C. Lamb, D. A. Lewis, D. Maomb, N. A. Porter, P. T.
Observation of TeV gamma rays from the Crab
nebula using the atmospheri Cerenkov imaging tehnique. Astrophysial
Reynolds and G. Vaanti.
Journal, vol. 342, no. 1, pages 379395, 1989. (Cited on page 7.)
[Weiÿ
et al. 2001℄ A. Weiÿ, N. Neininger, S. H 14 ttemeister and U. Klein. The eet
of violent star formation on the state of the moleular gas in M 82. Astronomy and Astrophysis, vol. 365, pages 571587, 2001. (Cited on page 63.)
[Wild
et al.
1992℄ W. Wild, A. I. Harris, A. Ekart, R. Genzel, U. U. Graf, J. M.
A multi-line study of the moleular
interstellar medium in M 82's starburst nuleus. Astronomy and AstroJakson, A. P. G. Russell and J. Stutzki.
physis, vol. 265, no. 2, pages 447464, 1992. (Cited on page 63.)
[Yao
et al.
2006℄ W. M. Yao, C. Amsler, D. Asner, R. M. Barnett, J. Beringer,
P. R. Burhat, C. D. Carone, C. Caso, O. Dahl and 160 o authors.
Review
Bibliography
of Partile Physis.
167
Journal of Physis G Nulear Physis, vol. 33, no. 1,
page 1232, 2006. (Cited on page 84.)
[Young & Soville 1984℄ J. S. Young and N. Z. Soville.
Moleular louds in M82.
Astrophysial Journal, vol. 287, no. 1, pages 153166, 1984.
(Cited on
page 63.)
Nonthermal Emission from a Radiobright Shell-Type Supernova Remnant IC 443. The Astrophysial Journal,
[Zhang & Fang 2008℄ L. Zhang and J. Fang.
vol. 675, no. 1, pages L21L24, 2008. (Cited on page 40.)
List of Figures
1.1
1.2
All-partile osmi ray spetrum. From [Beker 2008℄.
Main
physial
proesses
that
an
generate
. . . . . . . .
gamma-ray
2
photons
through dierent interationsm, both hadroni (b) and leptoni (,
d, e). Annihilation an take plae among leptons or hadrons.
1.3
. . . .
3
Skymap above 100 MeV from our Galaxy by the entire EGRET mission (phases 1 to 4), with the main soures deteted in gamma rays.
Credit: EGRET Team/NASA.
1.4
. . . . . . . . . . . . . . . . . . . . .
All-sky map above 300 MeV during the rst year of the
Fermi
LAT
telesope. Credit: NASA/DOE/Fermi LAT Collaboration. . . . . . .
1.5
Left:
5
6
Skymap RX J1713.7-3946 by H.E.S.S., blak ontours over-
plotted show the X-ray brightness that ASCA detetes from 1 to
3 keV. From [Aharonian
et al.
2004b℄.
Fermi
Right:
LAT spetral
energy distribution (SED) of the SNR W44, eah urve orresponds
to
π0
deay (solid), eletron bremsstrahlung (dashed), inverse Comp-
ton sattering (dotted) and bremsstrahlung from seondary eletrons
and positrons (thin dashed). From [Abdo
et al.
2010f℄
. . . . . . . .
9
1.6
Left: Skymap NGC 253 by HESS. Right: Spetrum M 82 by VERITAS. 13
1.7
Atual design of the IeCube neutrino detetor with 5160 optial sensors viewing a kilometer ubed of natural ie. The signals deteted
by eah sensor are transmitted to the surfae over the 86 strings to
whih the sensors are attahed. IeCube enloses its smaller predeessor, AMANDA. From IeCube Siene Team - Franis Halzen.
2.1
. .
15
SEDs generated by CR propagation in ISM with dierent properties.
M5 /d2kpc = 0.5.
Curve for D10 =
26
27
28
2
−1
10 , 10 , and 10
m s
are shown with solid, dotted, and dashed
Fluxes orrespond to a loud with
lines respetively.
Sensitivities of EGRET (red) and
Fermi
(blue)
(both for dierent diretions in the sky with dierent bakground
ontribution), H.E.S.S. (magenta) (survey mode and pointed observations with typial integrations), and MAGIC (yellow), are shown
for omparison purposes (see gure 1 of [Funk
et al.
2008℄ for details
on sensitivities). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22
LIST OF FIGURES
170
2.2
Examples of the model preditions for a hadroni maxima in the
1 − 100 GeV
regime.
The left top (bottom) panel shows the pre-
20 (30) p from an
M5 /d2kpc = 0.025 (0.04), loated at
4
4
aelerator of 10 (3 × 10 ) yr, diusing with
D10 = 1027 m2 s− 1.
The right top (bottom) panel urve shows the
ditions for a loud saled at
M5 /d2kpc = 0.08 (0.06) loated at
3
4
10 (20) p from an aelerator of 10 (10 ) yr, diusing with D10 =
28
2
−
2
10
m s 1. Inreasing the ratio M5 /dkpc , the urves move up mainpreditions for a loud saled at
taining all other features.
2.3
. . . . . . . . . . . . . . . . . . . . . . . .
24
For eah ombination of age and aelerator-target separation, for
whih more than two thousand spetra where numerially produed,
the energy of the maximum of suh spetra are shown in a ontour plot.
The olor of the dierent ontours orresponds to the
range of energy where the maximum is found aording to the olor
bar above eah gure.
From top to bottom, plots are reated for
the ase of an impulsive soure injeting protons in a medium with
D10 =1026 m2 s−1 , 1027 m2 s−1
2.4
and
1028 m2 s−1 .
. . . . . . . . . . .
26
The parameters for the plots are as follows, (top left) the dashed urve
t = 4×105 yr, R = 5 p, M5 /d2kpc = 0.01; the dashed urve
4
2
on the right: t = 10 yr, R = 20 p, M5 /dkpc = 0.1; (top right) the
6
2
dashed urve on the left: t = 2×10 yr, R=100 p, M5 /dkpc = 3; the
3
2
dashed urve on the right: t = 4×10 yr, R = 15 p,M5 /dkpc = 0.1;
6
(bottom left) the dashed urve on the left: t = 2×10 yr, R=15 p,
M5 /d2kpc = 0.004; the dashed urve on the right: t = 103 yr, R =
2
5 p, M5 /dkpc = 1; ( bottom right) the dashed urve on the left: t =
6
2
2×10 yr, R = 40 p, M5 /dkpc = 0.017; the dashed urve on the right:
4
t = 6×10 yr, R = 30 p,M5 /d2kpc = 2.5. D10 is set to 1026 m2 s−1 .
R is the aelerator-loud separation. . . . . . . . . . . . . . . . . .
on the left:
3.1
27
CO distribution around the remnant IC 443 (G189.1+3.0). The 3EG
gamma-ray soure J0617+2238 is plotted with white ontours. The
optial boundary of the SNR is superimposed as a blak ontour
[Lasker
et al.
1990℄.
The optial emission seems to fade in regions
where CO emission inreases. This indiates that the moleular material is likely loated on the foreground side of the remnant, absorbing the optial radiation. Plot taken from [Torres
10.
3.2
et al.
2003℄, gure
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
CR spetrum generated by IC 443 at two dierent distanes, 10 (solid)
and 30 (dashed) p, at the age of the SNR. Two types of aelerator
are onsidered, one providing a ontinuous injetion (blak) and other
providing a more impulsive injetion of CRs (red). The horizontal line
marks the CR spetrum near the Earth. The Y-axis units have been
hosen to emphasize the exess of CRs in the SNR environment. . . .
36
LIST OF FIGURES
3.3
171
MAGIC and EGRET measurement of the neighborhood of IC 443
(stars and squares, respetively) as ompared with model preditions.
The top (bottom) panel shows the results for an impulsive
(ontinuous) ase. At the MAGIC energy range, the top panel urves
show the preditions for a loud of 8000 M⊙ loated at 20 (1), 25
(2), and 30 (3) p, whereas they orrespond to 15 (1), 20 (2), 25
(3), and 30 (4) p in the bottom panel. At lower energies, the urve
shows the predition for a few hundred M⊙ loated at
3 − 4 p.
The
EGRET sensitivity urves (in red) are shown for the whole lifetime
of the mission for the Galati anti-entre (solid), whih reeived the
largest exposure time and has a lower level of diuse gamma-ray
emission, and for a typial position in the Inner Galaxy (dashed),
more dominated by diuse gamma-ray bakground.
The
Fermi
sensitivity urves (in blue) show the simulated 1-year sky-survey sensitivity for the Galati North pole, whih orresponds to a position
with low diuse emission (solid), and for a typial position in the
Inner Galaxy (dashed). These urves were taken from http://wwwglast.sla.stanford.edu/software/IS/glast_latperformane.html.
From [Rodríguez Marrero
3.4
et al.
2009℄.
. . . . . . . . . . . . . . . . .
38
Integrated photon ux as a funtion of time above 100 MeV and
100 GeV, solid (dashed) lines orrespond to the ase of the loud
loated at 10 (30) p.
The horizontal lines represent the values of
integrated uxes in the ase that the CR spetrum interating with
the loud is the one found near Earth. The vertial line stands for
the SNR age. EGRET and
Fermi
initially predited integral sen-
sitivity are shown, onsistent in value and olor oding with those in
Figure 3.3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1
39
Earlier MAGIC and EGRET (stars and diamonds, respetively), and
reent
Fermi
LAT and VERITAS (squares and upper trianges, re-
spetively) measurements of the neighborhood of IC 443 as ompared
with model preditions for an impulsive and a ontinuous aelerator, as onsidered in Chapter 3. The nominal values of parameters
for these models are the same as in Figure 3.3, although here the
dierent ontributions are summed up. See the text for details.
4.2
. . .
44
As in Figure 4.1, summed results (right) are produed by two main
omponents (left) oming from a giant loud in front of the SNR,
whih is at least partially overtaken by the diusing osmi rays
(∼5300 M⊙ at 10 p) and a loser-to-the-shell loud (at 4 p, with
350 M⊙ ), similar to the previous examples. The dotted and dashed
lines at the VHE range orresponds to dierent normalizations,
whih an also be understood as interating masses of
∼3200 M⊙ at the same distane.
D10 = 1026 m2 s−1 . . . . . .
fore,
∼4000
and
The diusion oeient is as be. . . . . . . . . . . . . . . . . . . .
46
LIST OF FIGURES
172
4.3
Cosmi-ray spetrum generated by the impulsive aelerator (IC 443)
at the two dierent loud distanes onsidered in Figure 4.2: 10 (solid)
and 4 p (dashed), at the age of the SNR, as a funtion of energy.
Dierent olors show results for dierent diusion oeients (blak,
D10 = 1026 m2 s−1 ;
and red,
D10 = 1027 m2 s−1 ).
The right panel
shows the ratio between the osmi-ray spetra of the left panel, and
the osmi-ray spetrum near Earth, as a funtion of energy.
4.4
Example of a model output with
D10 = 1027 m2 s−1 .
. . . .
47
The dierent
urves represent results for the loation of the giant moleular loud
at 10, 15, 20, 25, 30 p from the SNR shell, whereas the lose-to-theSNR loud is at 4 p. Neither in this nor in any other of the studied
models, the VHE soure spetrum an be reprodued by varying the
parameters with suh a diusion oeient sale. Furthermore, the
resulting SED in the
Fermi
LAT range is not hard enough to math
the data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5
47
Contour plot depiting the position of the peak of the SED generated by a 30 kyrs old injetion interating with louds at dierent
distanes, for a range of diusion oeient sale,
4.6
D10 .
. . . . . . . .
48
Examples of solutions around the disussed main values, exploring the
degeneraies (or unertainties) in determining the numerial values of
model parameters mathing the observational data. The order of the
panels in this plot, top to bottom and left to right, orresponds with
the parameters desribed in Table 4.5, being eah olumn one of the
4.7
et al. 2010℄. .
dierent δ parameters,
three groups therein. Adapted from [Torres
. . . . . .
Comparing gamma-ray yields with
from left
to right
δ = 0.4,
0.5, 0.6, and 0.7.
The other parameters are as in
Figure 4.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.8
49
52
Comparison (left) and ratio (right) of the ross setion parame-
δ-funtional form by
[Aharonian & Atoyan 1996℄, with that of [Kelner et al. 2006℄. . . . .
Left: Gamma-ray ux results using the [Kelner et al. 2006℄ approx-
terizations used in the previous Figures, the
4.9
53
imation for dierent distanes from the shell to the TeV-produing
loud, 10 (solid), 15 (dotted) and 20 (dashed) p. The lose-to-theremnant loud is xed at 4 p and ontains 350 M⊙ hanges in this
latter value do not improve the overall t. Right: Gamma-ray ux
results using the parameterization from [Kelner
et al.
2006℄ for dier-
ent values of the giant loud mass plaed at a xed distane of 10 p
(see text for details).
. . . . . . . . . . . . . . . . . . . . . . . . . .
53
4.10 Eletrons (eletrons and positrons are shown together), photons and
two avors of neutrinos produed within the louds onsidered nearby
IC 443, using a set of parameters shown in Figure 4.9 (right panel)
with mass of the giant loud equal to 7272 M⊙ . The
νµ
and
νe
neu-
trino urves show both the partile and the anti-partile ux. Data
should only be ompared with the photon urve.
. . . . . . . . . . .
54
LIST OF FIGURES
5.1
Code
173
ow
Q-diffuse,
of
[Torres & Domingo-Santamaría 2005℄
updates developed for this work.
5.2
to
adapted
take
into
from
aount
new
. . . . . . . . . . . . . . . . . . . .
60
Left: Comparison of the steady population of eletrons that would
result after solving the diuse loss equation injeting only primary
(solid blue) and only seondary (dashed blue) partiles from knokon and pion deay in the inner region of M82.
The total steady
eletron population (solid blak), resulting from the injetion of both
primary and seondary eletrons, is also shown.
Parameters used
in this Figure oinide with those presented later within the same
model (Figures 5.3 5.4). Right: Steady proton (solid) and eletron
(dashed) distributions in the innermost region of both M82 (blak)
and NGC 253 (red).
5.3
. . . . . . . . . . . . . . . . . . . . . . . . . . .
Multi-frequeny spetrum of M82 from radio to infrared.
65
The ob-
et al. 1988℄ (triangles),
et al. 2003℄ (squares), and
servational data points orrespond to: [Klein
[Hughes
et al.
1994℄ (irles) and [Förster
referenes therein in eah ase.
spond to:
The results from modelling orre-
synhrotron plus free-free emision (dashed), dust emis-
sion (dotted) splitted in a ool (blue, Tc
(purple,Tw
≃ 200 K)
and a warm
omponent, and the total emission from radio
and IR emission (solid).
5.4
= 45 K)
. . . . . . . . . . . . . . . . . . . . . . . . .
66
Left: Energy distribution of the dierential gamma-ray uxes, exploring a range of unertainties in supernova explosion rate and utos
in the primary energy, as it is explained in the text.
tivity urves for EGRET (red),
from [Funk
et al.
Fermi
The sensi-
(blue), MAGIC (purple), all
2008℄, and the intended one for the forthoming
Cerenkov Telesope Array (CTA, violet) are shown. Right: Dierential neutrino ux preditions from the inner region of M82, total and
separated in dierent hannels.
The neutrino preditions make use
of the same explored parameters already presented in the left panel
and explained in the text.
5.5
. . . . . . . . . . . . . . . . . . . . . . . .
67
Comparison of the multi-wavelength preditions for dierent initial
spetral slope in the injetion, see Figure 5.3 for further details. The
blak urve orrespond to the model with proton injetion spetrum
p = 2.1
B = 130µG, whereas the red urve orrespond to the results of modelling with p = 2.3 and B = 170µG. The
gamma-ray emission from the −2.3 model in the ase of the highest
and magneti eld
SN explosion rate is shown against those obtained with the harder
injetion (the green shadow, oming from the unertainties desribed
before). Main dierenes appear at high energies. . . . . . . . . . . .
5.6
71
Dierent ontributions to the radio emission (synhrotron + freefree) by the steady primary-only (blue) and seondary-only (yellow)
eletron population, also ompared to the total radio emission of the
whole eletron population (blak).
. . . . . . . . . . . . . . . . . . .
72
LIST OF FIGURES
174
5.7
Energy distribution of the dierential gamma-ray uxes of M82, exploring a range of unertainties in supernova explosion rate and efieny to injet energy from SN to CR. The shaded green area
orresponds to the original model presented in this Chapter and
et al.
[de Cea del Pozo
2009b℄.
Data points and upper limit orre-
spond to both VERITAS (stars) and
5.8
Multifrequeny
spetrum
of
NGC
Fermi
253
(diamonds) detetions. .
from
radio
The observational data points orrespond to:
angles),
[Ott
[Elias
et al.
et al.
1978℄ (irles),
[Rieke
to
76
infrared.
[Carilli 1996℄ (tri-
et al.
1973℄ (asterisks),
2005℄ (diamonds) and [Teleso & Harper 1980℄ (squares),
and referenes therein.
The results from modelling orrespond to:
synhrotron plus free-free emission (dashed), dust emission (dotted)
splitted in a ool (blue, Tcold = 45 K) and a warm (purple, Twarm
∼ 200 K)
omponent, and the total emission from radio and IR emis-
sion (solid).
5.9
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
77
Energy distribution of the dierential gamma-ray uxes of NGC 253,
exploring the unertainty in distane, a range of timesale diusion
(τ0 ) and possible utos in the proton injetion spetrum. The original model from [Domingo-Santamaría & Torres 2005℄ is also shown
for omparison, as well as data points from
Fermi
detetion (dia-
monds) and the integral ux from the H.E.S.S. detetion (square),
transformed in dierential ux (assuming a range of injetion spetra). 78
6.1
Polarization of the medium by a harged partile with (a) low veloity,
v < c/n,
and (b) high veloity,
Cherenkov wavefront in ()
6.2
Sheme of a
γ -ray
v > c/n.
Huygens onstrution of
. . . . . . . . . . . . . . . . . . . . . . .
indued eletromagneti shower (right) and a
hadron-indued shower (left) developing in the atmosphere . . . . . .
6.3
84
Image formation sheme in the amera of an IAC telesope.
values are referred to a 1 TeV
γ -indued
85
The
shower. The blue part is the
image head whereas the red part is the image tail. The numbers in
the pixels orrespond to the number of inident photons. [Tesaro 2010℄ 87
6.4
Piture of the two MAGIC telesopes: MAGIC-I (left) and MAGIC-II
(right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.5
Sheme for the standard trigger onguration in MAGIC I (left) and
II (right) ameras ([Meui
6.6
89
et al.
2007℄, [Cortina
et al.
2009℄). . . . .
90
Sketh of the denition of the signal (ON) and bakground (OFF)
regions in
wobble
observations. The anti-soure is the OFF position
loated symmetrially to the ON position (the red irle) with respet
to the enter [Mazin 2007℄. . . . . . . . . . . . . . . . . . . . . . . . .
6.7
92
Graphial representation of some of image parameters desribed in
the text.
The nominal position of the observed soure is (x0 , y0 )
[Mankuzhiyil 2010℄. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
95
LIST OF FIGURES
6.8
Sketh of a
175
tree
struture for the lassiation of an event
length and width.
The deision path through the
tree,
v
via size,
leading to
lassiation of the event as hadron an be followed [Errando 2009℄. .
7.1
Radio image of the region around SNR G65.1+0.6.
objets are:
97
The numbered
(1) 3EG J1958+2909, (2) 2 CG 065+00, (3) 0FGL
J1954+2838, (4) 0FGL J1958.1+2848, (5) region of dierent spetral index, (6) IRAS 19520+2759, (7) bright ompat radio objet.
7.2
.
102
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
105
Observation setup for the two
Fermi
soures J1954 and J1958 in the
ontext of SNR G65.1+0.6 and a Milagro signiane ontour. J1958
appears only in one wobble position (W1), so the OFF data is taken
from the other wobble sample, using the same position relative to
the pointing diretion. The outline of the remnant is taken from the
et al. 1990℄. The extension of the Milagro
signiane ontour [Abdo et al. 2009i℄ is ompatible with their point
radio map in [Landeker
spread funtion.
7.3
2
Plots showing the θ distributions for J1954 (left) and J1958 (right).
The shapes of the ON and OFF distributions agree well with eah
other in both soures, whih means there is no
dashed lines indiate the signal regions.
7.4
γ−ray
signal.
The
. . . . . . . . . . . . . . . .
106
Skymaps of the exess events (top) and signiane (bottom) for
J1954 (left) and J1958 (right). The blak star shows the enter of the
pointed soure, the white irle represents the MAGIC point spread
funtion (PSF) at mid energies. The distribution of signianes are
well-tted with a simple gaussian. . . . . . . . . . . . . . . . . . . . .
7.5
Compilation
1FGL
of ux
measurements
J1954.3+2836
from
and
Fermi
upper limits
[Saz Parkinson
for:
(left)
et al.
2010,
107
et al. 2010a℄ , (right) 1FGL J1958.6+2845 from EGRET
et al. 1999℄, Fermi [Abdo et al. 2010b, Abdo et al. 2010a℄,
together with MAGIC and Milagro [Abdo et al. 2009i℄ data. The 3%
fration of the MAGIC Crab spetrum [Albert et al. 2008b℄ is shown
Abdo
[Hartman
for omparison. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1
110
Konrad Bernlöhrs adapted layout of the original ultra-CTA (from
Padova 2008 CTA meeting). Four types of telesopes are plotted, see
table 8.1 for details, being 1 = red, 2 = green, 3 = blue and 4 =
magenta. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.2
112
Layout ongurations of the three representatives: B (left), D (enter), I (right).
The types of telesopes orresponds to the ones de-
tailed in Table 8.1, being 1 (red), 2 (green), 3 (blue), 4 (magenta), the
number in brakets orresponds to the eld of view of eah telesope. 113
8.3
Dierential sensitivity of the three representative ongurations: D
(red), B (blue), I (green), in Crab units (C.U.) for 50 hours of observation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
114
LIST OF FIGURES
176
8.4
Angular resolution (80% ontainment radius) of the three representative ongurations, see Figure 8.3, for best resolution (left) and best
sensitivity (right). . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.5
Energy resolution of the three representative ongurations, see Figure 8.3, for best resolution (left) and best sensitivity (right). . . . . .
8.6
114
Total gamma ray emission from a moleular loud of mass
loated at a distane of 1 kp.
115
105 M⊙
The distane between the moleu-
lar loud and the SNR is 50, 100 and 200 p for left, enter and
right panel, respetively.
The solid, dotted, and dashed lines refer
to the emission at 2000, 8000 and 32000 years after the SN explosion. Private ommuniation from S. Gabii, based on gure 5 from
[Gabii
8.7
et al.
2009℄. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gamma-ray emission from a moleular loud of
105 M⊙
116
illuminated
by an aelerator (whih explosion ourred 2000 yrs ago) and simulated with layout onguration I, for 20 hours of observation. The
moleular loud is loated at a distane of 1 kp from the observer
and plaed at dierent distanes from the aelerator: 50 (blak), 100
(blue), 200 (red) p.
8.8
. . . . . . . . . . . . . . . . . . . . . . . . . . .
117
Spetral modeling of the gamma-ray emission of the two losest starburst galaxies M82 (left) and NGC 253 (right). The overlaid blue box
orresponds to the range of energies that CTA is predited to observe
∼ 100 TeV). Data points in both plots
Fermi (diamond), VERITAS (star) and
Figures taken from [de Cea del Pozo et al. 2009a℄.
(from a few tens of GeV to
orrespond to detetions by
H.E.S.S. (square).
For a omplete explanation, see Chapter 5.
8.9
. . . . . . . . . . . . . .
119
M82 spetrum as simulated for CTA for 30 hrs with onguration B
(top), D (enter), I (bottom). The grey points orrespond to observational data: at lower energies, an upper limit (68% .l.) from
Fermi,
and at higher energies, the dierential data points and an upper limit
(99% .l.) from VERITAS. . . . . . . . . . . . . . . . . . . . . . . . .
121
8.10 NGC 253 spetrum as simulated for CTA in 50 (left) and 70 hours
(right) with onguration D. The observational data (grey) orresponds to an upper limit (68% .l.) from
Fermi ; and H.E.S.S. integral
data point (onverted to dierential ux) . . . . . . . . . . . . . . . .
122
LIST OF FIGURES
9.1
177
Sky map of gamma-ray andidate events (bakground subtrated)
in the diretion of MAGIC J0616+225 for an energy threshold of
about 150 GeV in galati oordinates. Overlayed are
12 CO emission
ontours (yan) showing the position of their maxima oiniding with
the MAGIC detetion, and ontours of 20 m VLA radio data (green),
12 rple) and gamma-ray ontours from
X-ray ontours from Rosat (pu
EGRET (blak). The white star denotes the position of the pulsar
CXOU J061705.3+222127. The blak dot shows the position of the
1720 MHz OH maser. The white irle shows the MAGIC I PSF of
σ = 0.1◦ .
9.2
From [Albert
et al.
2007b℄
. . . . . . . . . . . . . . . . . .
126
Loations and extensions of the 4 gamma-ray soures. Centroid positions are marked with dierent symbols: EGRET (blue triangle),
MAGIC (red downside triangle), VERITAS entroid (green star) and
Fermi
LAT (blak diamond). The respetive loalization errors are
shown as rosses.
Best-t spatial extensions of the
Fermi
(ross-
hathed band) and VERITAS (striped green band) soures are drawn
as rings with radii of
ext
θ68
and widths of
±1 σ
error. The PWN loa-
tion is shown as a magenta dot. Contours are the loations and shapes
of the loal shoked moleular louds taken from [Huang
Figure taken from [Abdo
9.3
et al.
2010g℄
et al.
1986℄.
. . . . . . . . . . . . . . . . .
127
2
Plot showing the θ distribution for the MAGIC soure in the region
of IC 443. The shapes of the ON and OFF distributions agree well
with eah other. A hint of signal is already seen in barely 3 hours of
observations.
9.4
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
130
Skymap (map of signianes) of the SNR IC 443 (left) and distribution of signianes (right) of the same region. The blak ross marks
the position of the MAGIC soure J0616+225. The white irle shows
the PSF of the MAGIC stereo system.
9.5
. . . . . . . . . . . . . . . . .
131
CTA simulated spetrum of IC 443 with onguration I (green urve)
and 50 hours. The input spetra (grey lines) orrespond: at lower energies to the power law published from
Fermi
above 3 GeV, whereas
at higher energies the power law index is taken from the measurements by MAGIC and VERITAS. The grey symbols show the atual
data from previous experiments. The simulated data points for CTA
above 100 GeV an be tted to a power law, whih index depends
on the assumed initial spetra (blak dots for MAGIC, blue ones for
VERITAS).
9.6
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
132
The spetrum of IC443 is simulated with layout CTA-I for 50 hours of
observation, assuming an input spetrum in the form of a power law
with a ut o of 5 (top) and 10 (bottom) TeV. The power law index is
the one published by MAGIC (-3.1). The highest energy ut-o that
ould be resolved is at 5 TeV, at higher energies (i.e. 10 TeV) a tting
with power law with a ut o (red) is statistially undistinguishable
from a simple power law (green) in the observed CTA range of energies.134
List of Tables
1.1
Mission parameters of the three latest spae telesopes in the MeV GeV range: EGRET, AGILE and
Fermi
LAT. The sensitivity above
100 MeV is onsidered for a 2-year survey at high latitudes.
1.2
. . . . .
6
Performane of the three main Cherenkov experiments in the GeV
TeV range: H.E.S.S., MAGIC and VERITAS. In the title:
♯
Tels.
stands for number of telesopes, Tels. Area is the area of eah telesope, f.o.v. is the eld of view, Tot. Area is the total area of the array
of telseopes, Eth is the energy threshold, Ang. res. means angular
resolution, and Sensitivity 50 h onveys the soure ux in 50 hours of
observation respet to the Crab Nebula ux with a signiane of 5
sigma. From [De Angelis 2011℄. . . . . . . . . . . . . . . . . . . . . .
2.1
Dependene of the SED (E
(ont.)
2 F vs.
E)
8
Imp.
on various parameters.
stands for the impulsive (ontinuous) aelerator ase.
De-
pendenes upon loud parameters suh as density (nCl ), mass (MCl ),
and radius (RCl ) are obvious and related.
4.1
. . . . . . . . . . . . . . .
23
Main model parameters for solutions shown in Figure 4.6, exept
model 3, whih instead is shown in Figure 4.2.
DGM C
and
dsnr
are
the distane to the GMC and the loser-to-the-SNR moleular louds.
The three quoted
f
values dene
MGM C = (1/f ) 8000 M⊙ .
The three
groups explore dierent degeneraies: in the position of the GMC, in
the position of the smaller loud, and on the diusion oeient.
5.1
. .
51
Physial parameters used in the multi-wavelength model of M82, presented in the previous setion and in [de Cea del Pozo
et al.
2009b℄,
together with spei values that try to math the emission from the
VERITAS detetion.
In any ase, the (small) variations explored
below are within the former preditions of the original model. The
list of parameters is divided in setions: observational values, derived
from observational values, obtained from modelling, and assumed.
SB stands for starburst.
5.2
Physial
of
NGC
parameters
253,
. . . . . . . . . . . . . . . . . . . . . . . . .
used
as
in
the
presented
[Domingo-Santamaría & Torres 2005℄
multiwavelength
both
in
study
and
the
in
75
model
previous
this
setion,
but exploring some variations allowed within the model in order
to math the emission from the H.E.S.S. detetion.
The list of
parameters is divided in setions: observational values, derived from
observational values, obtained from modelling, and assumed.
stands for starburst.
SB
. . . . . . . . . . . . . . . . . . . . . . . . . . .
79
LIST OF TABLES
180
7.1
Dierential upper limits for both soures, for the present rosshek
analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.2
Charateristi parameters of the two Fermi pulsars 1FGL
2836
and 1FGL
J1958.6 + 2845,
108
J1954.3 +
refereed as J1954 and J1958, respe-
tively. See referenes in the text.
. . . . . . . . . . . . . . . . . . . .
109
8.1
Main harateristis of dierent types of telesopes for CTA. . . . . .
112
8.2
Summary of the observational detetions of M82 and NGC 253 by
Fermi
(at high energies, HE), VERITAS and H.E.S.S. (very high en-
ergies, VHE). The energy thresholds for the integral ux alulations
are: above 100 MeV in the ase of
Fermi
LAT observations, above
700 GeV for VERITAS, and above 220 GeV for H.E.S.S.
9.1
Power law (p.l.)
. . . . . . .
119
index for MAGIC-like or VERITAS-like spetrum
for IC 443, when simulating CTA response for 50 hrs in onguration I.131
9.2
Statistis of two ttings to the spetrum for IC 443, when simulating
CTA response for 20 hrs in onguration I. The simulated data points
use the intrinsi spetra from Figure 9.6: a power law with a ut o
at a few TeV. The two ttings, then, are a power law with or without
a ut o. The rst number is the t probability, whih values should
be in the range between
5 − 60%,
the losest to
The seond set of numbers represents the redued
50%, the better.
χ2 (dened as χ2
divided by the number of degrees of freedom), and for a good t, it
should be loser to 1. . . . . . . . . . . . . . . . . . . . . . . . . . . .
133
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