Observational and theoretical study of the point sources of very high energy γ-ray emission by M.Sc. Iurii Babyk A thesis is submitted to Dublin City University for the degree of Doctor of Philosophy in the School of Physical Sciences Supervisors: Dr. M. Chernyakova, Prof. G. Hughes January 2017 Declaration of Authorship I hereby certify that this material, which I now submit for assessment on the programme of study leading to the award of Ph.D. is entirely my own work, and that I have exer- cised reasonable care to ensure that the work is original, and does not to the best of my knowledge breach any law of copyright, and has not been taken from the work of others save and to the extent that such work has been cited and acknowledged within the text of my work. Signed: ID No.: Date: i Acknowledgements I would like to thank my thesis supervisor Dr. Masha Chernyakova, she has always been willing to take the time to discuss in great depth our own research area and many other interesting research areas. Every time we have met, I have been inspired a lot by her great scientific insights. I must also thank Masha for her patience in explaining to me the varying scientific aspects of my thesis. In addition, I enjoyed going to parties in her home with Masha’s family, and I will never forget the delicious dishes she prepared for me being a student. It is my great pleasure and honor to get to know Masha during these years, trust this will continue into the future. In DCU, I would like to thank all of the wonderful staff of School of Physical Sciences, namely Prof. Enda McGlynn, Prof. Greg Hughes, Prof. Colette McDonagh, physics dept secretary Lisa Payton, plus all the staff lectures and graduate students in the School of Physical Sciences. People that I met during conferences and seminars were more than helpful to me, the list would be far too long to name one by one, but I would like to say a big thank you here to all of them. I would also like to thank my examiners, Prof. Joern Willms and Prof. Eugene Kennedy under which guidance thesis got the much improved current shape. In DIAS, I would like to thank the staff in the Dublin Institute for Advanced Studies, namely the School of Cosmic Physics Director, Head of the Astronomy & As- trophysics Section, Senior Professor Prof. Luke O’C Drury, Prof. Tom Ray, Prof. Felix Aharonian, who have taken care of me while in the Section. To the IT personnel, I would also like to thank Philippe and Dmitrii, who helped me with my computer issues. My thanks also go out to the very helpful staff members, Anne Grace-Casey and Eileen Flood. Finally, thank you to all the School fellows, post docs and scholars for all their formal and informal discussions both of a scientific and non scientific nature. The number of people in DIAS and DCU whom I would like to thank is so big, that probably the whole volume of this thesis would not be enough to fit everybody in. I mentioned only briefly very few of them and would like to ask all the others to forgive me their absence in this acknowledgment. I remember all of you and you always will be in my heart. I would like to voice my gratitude to my Ukrainian advisor Dr. Irina Vavilova at the Main Astronomical Observatory of National Academy of Science of Ukraine for her guidance and continuous support during these years. I want to thank Dr. Ievgen Vovk ii at the Max-Planck Institute fur Physics for his encouragement and numerous discussions over skype, in Ireland and Ukraine during my academic career. Thanks to Dr. Mike Hogan for correcting the numerous English mistakes I made during the writing of this thesis. Last but not least, I can not forget Hilary O’Donnell/Sullivan, during my Ph.D. she was my real local mother, my Irish Mother, who cares about me in DIAS and Dun- sink Observatory, providing me a nice possibility to improve my English skills getting involved and meeting with lots of people through the outreach program in Dunsink Ob- servatory. Finally, and most importantly, this work would not have been possible without the endless support and encouragement from my lovely wife, parents, family and friends. iii Contents Declaration of Authorship i Acknowledgements ii Contents iv Abstract vii 1 From X-ray binaries to gamma-ray binaries 1 1.1 X-ray binaries .................................. 2 1.1.1 Neutron stars .............................. 6 1.1.2 X-ray pulsars in binaries ........................ 10 1.1.3 Gamma-ray pulsars .......................... 14 1.2 Gamma-ray binaries .............................. 18 1.3 Summary .................................... 27 2 Observations and data analysis 29 2.1 Atmospheric windows ............................. 29 2.1.1 Historical review of X-ray astronomy ................. 31 2.2 XMM-Newton X-ray Observatory ....................... 33 2.2.1 Analysis of XMM-Newton X-ray Data ................ 36 2.3 Chandra X-ray Observatory .......................... 41 2.3.1 Analysis of Chandra X-ray Data ................... 44 2.4 Suzaku X-ray Observatory ........................... 44 2.4.1 Analysis of Suzaku X-ray Data .................... 47 2.5 Swift X-ray Observatory ............................ 47 2.5.1 Analysis of Swift X-ray Data ..................... 48 2.6 Fermi Gamma-ray Observatory ........................ 49 2.6.1 Analysis of Fermi X-ray Data ..................... 51 2.7 X-ray spectral analysis ............................. 52 2.7.1 χ2 and C statistics ......................... 54 − − 2.7.2 Parameter measurements ....................... 55 3 High-energy processes in gamma-ray binaries 59 3.1 Compton scattering .............................. 59 iv 3.2 Synchrotron emission .............................. 62 3.3 Bremsstrahlung emission ............................ 65 3.4 Calculation of losses .............................. 66 3.4.1 Electron losses during inverse-Compton scattering ......... 66 3.4.2 Electron losses during synchrotron radiation ............. 69 3.4.3 Energy losses of electrons during ionization ............. 71 3.4.4 Results of calculations ......................... 73 4 X-ray and Gamma-ray observations of PSR B1259 63 75 − 4.1 The XMM-Newton observations ........................ 75 4.2 The Chandra observations ........................... 77 4.3 The Suzaku observations ............................ 79 4.3.1 Broadband spectra of PSR B1259 63 Suzaku observations ..... 82 − 4.4 The Swift observations ............................. 86 4.5 The Fermi/LAT observations ......................... 90 5 Interpretation of results of PSR B1259 63 92 − 5.1 The orbital lightcurves ............................. 92 5.2 Fast variability in the lightcurve ....................... 94 5.3 The modeling of the X-ray double-peaked lightcurve ............ 96 5.4 Explanation of the GeV flare in PSR B1259 63 ............... 99 − 5.4.1 Evolution of the Be-type star disk mass and size based on the optical observations ..........................101 5.4.2 High-energy consequences of the Be-type star disk disruption . 102 6 X-ray observations of LS I +61◦ 303 105 6.1 The Suzaku observations ............................105 6.1.1 Timing analysis .............................106 6.1.2 Spectral analysis ............................107 6.2 The XMM-Newton observations ........................110 6.2.1 Timing analysis .............................112 6.2.2 Spectral analysis ............................115 6.3 The Swift observations .............................116 6.4 The Chandra observations ...........................117 7 Interpretation of results of LS I +61◦ 303 122 7.1 The modulation of X-ray flare .........................122 7.2 The variability of LS I +61◦ 303 lightcurve .................125 7.3 The variability of hydrogen column density of LS I +61◦ 303 .......126 8 Conclusions and future prospects 129 A Monte Carlo simulations of PSR B1259 63 spectra 133 − v B Monte Carlo simulations of XMM-Newton lightcurves for LS I +61◦ 303. 156 Bibliography 163 vi Observational and theoretical study of the point sources of very high energy γ-ray emission Iurii Babyk Abstract The study of the sky using the most energetic photons plays a crucial role in de- tecting and exploring high-energy phenomena in the Universe. Observations conducted over recent years with new ground-based and space-borne gamma-ray instruments re- veal that the universe is full of extreme accelerators, i.e., objects with surprisingly high efficiency for acceleration of electrons. In particular such an efficient acceleration is ob- served in gamma-ray-loud binary (GRLB) systems. GRLBs are a newly identified class of X-ray binaries in which interaction of an outflow from the compact object with the wind and radiation emitted by a companion star leads to the production of very-high-energy gamma-ray emission. Only five such systems have been firmly detected as persistent or regularly variable TeV gamma-ray emitters. All GRLBs detected in the TeV energy range contain a hot, young star and exhibit variable or periodic emission at multiple wavelengths across the electromagnetic spectrum. Details of the physical mechanism of the high-energy activity of GRLBs are not clear yet. Broad multi-wavelength observations are crucial to reveal the character- istic energies of the relativistic wind and better understanding of the nature of these sources. It looks quite possible that all these systems can be understood within the “hidden pulsar” model, and the observed differences are due to the different sizes of the system. In my work, I concentrate on the X-ray and gamma-ray emission observed from gamma-ray binaries PSR B1259 63 and LS I +61◦ 303 with Suzaku, XMM-Newton, − Swift, Chandra and Fermi observatories. In PSR B1259 63, the compact source is a − vii young 48 ms radio pulsar orbiting Be-type star with period of 3.4 years. During my stud- ies, I have been intensively involved in the analysis of the results of two multi-wavelength campaigns organized in 2010 and 2014 during the periastron passages in this system.