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Universitat Aut` onoma de Barcelona
Doctoral Thesis
Gamma-ray emission of young stellar
objects and discovery of superorbital
variability at high energies
Author:
Daniela Hadasch
Supervisors:
Prof. Dr. Diego F. Torres
Prof. Dr. Lluis Font Guiteras
A thesis submitted in fulfilment of the requirements
for the degree of Doctor of Physics
in the
Universitat Aut`onoma de Barcelona
Department of Physics
June 2013

Declaration of Authorship
I, Daniela Hadasch, declare that this thesis titled, ’Gamma-ray emission of young
stellar objects and discovery of superorbital variability at high energies’ and the work
presented in it are my own. I confirm that:
This work was done wholly or mainly while in candidature for a research degree
at this University.
Where any part of this thesis has previously been submitted for a degree or any
other qualification at this University or any other institution, this has been clearly
stated.
Where I have consulted the published work of others, this is always clearly at-
tributed.
Where I have quoted from the work of others, the source is always given. With
the exception of such quotations, this thesis is entirely my own work.
I have acknowledged all main sources of help.
Where the thesis is based on work done by myself jointly with others, I have made
clear exactly what was done by others and what I have contributed myself.
Signed:
Date:
i

UAB
Abstract
Department of Physics
Doctor of Physics
Gamma-ray emission of young stellar objects and discovery of superorbital
variability at high energies
by Daniela Hadasch
This thesis is structured in three parts: 1.) Observations of binary systems with the
Fermi satellite and discovery of superorbital modulation at high energies. 2.) Studies of
the so-called magnetars at high and at very high energies and finally 3.) we are giving
prospects for the future of the field at very high energies.

Contents
Declaration of Authorship i
Abstract ii
Resumen v
Summary vii
1 High and Very High Energy γ-ray Astrophysics 1
1.1 What are γ-rays?................................ 1
1.2 How are γ-rays produced? . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Where are γ-rays coming from? . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3.1 Galactic Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.2 Extragalactic Sources . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 High and Very High Energy γ-Ray Detection 10
2.1 Imaging Air Cherenkov technique . . . . . . . . . . . . . . . . . . . . . . . 10
2.1.1 Current IACT experiments . . . . . . . . . . . . . . . . . . . . . . 12
2.2 Principles of a pair conversion telescope . . . . . . . . . . . . . . . . . . . 14
2.2.1 Current instruments . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3 PART I: Gamma-ray binaries 18
3.1 Overview and Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2 2.5 years monitoring of LS 5039 and LS I +61◦303 with the Fermi Large
Area Telescope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2.1 The observed sources . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.2 Analysis settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.3 Spectral analysis methods . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.4 Timing analysis methods . . . . . . . . . . . . . . . . . . . . . . . 22
3.2.5 LS 5039 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2.5.1 Orbitally averaged spectral analysis . . . . . . . . . . . . 23
3.2.5.2 Phase-resolved analysis . . . . . . . . . . . . . . . . . . . 24
3.2.5.3 Lightcurve . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.2.6 LS I +61◦303 Results . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.2.6.1 Orbitally averaged spectral analysis . . . . . . . . . . . . 25
3.2.6.2 Lightcurve . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.2.6.3 Phase resolved spectral analysis . . . . . . . . . . . . . . 31
iii

Contents iv
3.2.6.4 Spectral fitting . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2.6.5 2.5 years of contemporaneous Radio and GeV data . . . . 32
3.2.6.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.3 LS I +61◦303 Longterm Gamma-Ray Variability . . . . . . . . . . . . . . . 33
3.3.1 Data and Analysis settings . . . . . . . . . . . . . . . . . . . . . . 34
3.3.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.3.3 Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.3.4 Multi-wavelength context . . . . . . . . . . . . . . . . . . . . . . . 42
3.3.4.1 X-rays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.4 Pulsed fraction for high mass X-ray binaries . . . . . . . . . . . . . . . . . 46
3.4.1 Comparison of the limits with X-ray pulsed fractions of known
pulsars.................................. 47
4 PART II: Magnetars 54
4.1 Overview and motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.2 Magnetars observations at TeV with the MAGIC telescopes . . . . . . . . 56
4.2.1 The observed magnetars . . . . . . . . . . . . . . . . . . . . . . . . 56
4.2.2 Analysis and Data . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.2.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.3 Magnetars observations at GeV with the Fermi Large Area Telescope . . 61
4.3.1 Observation and data reduction . . . . . . . . . . . . . . . . . . . . 61
4.3.2 Likelihood analysis and results . . . . . . . . . . . . . . . . . . . . 62
4.3.3 Sources with high TS values . . . . . . . . . . . . . . . . . . . . . . 63
4.3.4 Upper limits evaluation . . . . . . . . . . . . . . . . . . . . . . . . 65
4.3.5 Timing analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.3.6 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 66
5 PART III: Prospects 68
5.1 Description of CTA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.2.1 CTA flux error reduction in known TeV sources . . . . . . . . . . . 73
5.2.2 Short timescale flux variability . . . . . . . . . . . . . . . . . . . . 76
5.2.3 Sensitivity to spectral shape variations . . . . . . . . . . . . . . . . 78
5.2.4 Exploring the colliding winds of massive star binary systems . . . 79
5.3 Summary and conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
Bibliography 81