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Understanding the Magnetic Field Configuration in X-Ray Pulsars

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Understanding the magnetic field configuration in X-ray pulsars through spectroscopy and polarimetry Varun Under the supervision of Prof. Biswajit Paul Department of Astronomy & Astrophysics Raman Research Institute, Bangalore, India. This dissertation is submitted for the degree of Doctor of Philosophy to Jawaharlal Nehru University, New Delhi, India. August 2019 To my family and friends. And to an average person who wants to dream and achieve. Declaration I hereby declare that the work presented in this thesis titled, "Understanding the magnetic field configuration in X-ray pulsars through spectroscopy and po- larimetry" is the result of the investigations carried out by me under the supervision of Prof. Biswajit Paul at the Astronomy and Astrophysics Group, Raman Research Institute, Bengaluru, India. I further declare that the work presented in this thesis has not been submitted for the award of any other degree or diploma of any other University or Institution. Keeping with the general practice, due acknowledgements have been made wherever the work described is based on other investigations. I have also run the thesis through the Turnitin software. Prof. Biswajit Paul Varun Thesis Supervisor Astronomy and Astrophysics Raman Research Institute Bengaluru - 560080 Certificate This is to certify that the dissertation entitled "Understanding the magnetic field configuration in X-ray pulsars through spectroscopy and polarimetry" sub- mitted by Varun for the award of the degree of Doctor of Philosophy to Jawaharlal Nehru University, is his original work. This has not been submitted or published for any other degree or qualification to any other university. Prof. Ravi Subrahmanyan Prof. Biswajit Paul Director Thesis Supervisor Raman Research Institute, Bengaluru 560 080 INDIA. Acknowledgements I want to thank the whole RRI for being my home and workplace for all these years. I really enjoyed the natural environment and relaxed work culture here. All the staff members are extremely helpful, prompt, and generous. I thank my supervisor, Prof. Biswajit Paul for introducing me to the high energy instrumentation and observations. He has been very supportive and patient through- out this journey. He has always come to my aid at critical times. He has always been available for sending feedbacks and clarifying my doubts. I would also like to thank my thesis advisors Prof. Shiv Sethi and Dr. Ramesh Balasubramanyam, for their support, encouragement, and timely feedback. They have helped me grow as a researcher. I want to thank all the members of X-ray lab: Rishin Ji, GK Ji, Rajagopal Sir, Abhilash, Sandhya P., Pooja Verma. Rishin ji has been very helpful for all the guidance and help in my instrumentation work. It is amazing to work with him. GK Ji has been very a helpful and cheerful company in the lab. I thank Rajgopal sir for his help in the lab. During my experiments, Abhilash has been a great company from time to time. I want to thank Vidya for treating me with love and affection. Her presence in the department always gave me a homely feeling. She has really been very helpful for planning all my national and international travels. She always kept me aware of all official procedures and suggested the best options. After Vidya was shifted to admin- istration department, Harini has also been very helpful and prompt. I would like to thank Lakhmi amma, Hanmantappa, and Gangadhar their help in keeping my sitting place neat and clean. I have really become fond of tea and coffee made Lakshmi amma. I want to thank the computer department staff for technical support. Jacob, Krish- namurthy, and Sridhar have always been very prompt for any software and hardware related issues. Also, I would like to thank the administration staff for their help and quick response in handling all the official matters. x I want to thank my parents for their love and affections. Both of them have given me full freedom to pursue my life and have always been there for me. My father always allowed me to make independent decisions, and that has helped me to become fearless. My mother has been a great source of inspiration throughout my Ph.D. My wife Anjali is the most pleasant addition to my life during last one year. She really has been very accommodating and adjusting for my hectic working schedule. I want to thank all the students in the department for their help and engaging discussions. I shared many memorable moments during our conversations on lunch or tea time. My batch mates Sourabh and Janakee were a cheerful company during the course work. I have shared many laughs with all my roommates in the department – Abir, Raj, Karam, Priyanka, Nazma, Naveen, Karthik, Hemanth, Sanhita, Saikat, and Angnibha. I am proud of being a member of "Noisy Corner" in the department. I thanks all my seniors (Chandreyee, Nazma, Gayathri, Aru, Pragati, Nirmal) for sharing their knowledge with me. For general counseling on any matter, I have al- ways reached to Nazma or Gayathri. I have learned a lot from Nirmal Iyer, who was a postdoc in the department. His curious nature and creativity really inspired me. Chandreyee has been really great collaborator. I thank my juniors Sanhita, Hemanth and Ashwin. I have gained a lot to confidence about my own abilities in my research field by discussing with them. My time in RRI, would not have been a pleasant one without hostel friends. I thank Deepak, Raj, Nomaan, Rahul, Nancy, Amrita, Chaitra, Reena, and Anand for being such a great company of mutual interest and values. Spending time with them really kept my mood positive. I would like to thanks all the members of RRI Cricket club for being an amazing company. Also, I learned some new sports after coming to Bengaluru. I thank my running, cycling, and swimming partners Nomaan and Raj. I leaned a lot, and had a great time with Simon in the Gym. I thanks Adit for teaching me tennis. Table of contents Abstract xv Synopsis xvii List of Publications xxv List of figures xxvii List of tables xxxv 1 Introduction 1 1.1 Introduction................................. 1 1.2 Cyclotron Resonance Scattering Feature . .... 3 1.3 Recent significant results in cyclotron line research . .......... 7 1.4 Polarimetry in high energy astrophysics . ..... 13 1.5 Science Prospects of Polarimetry in High Energy . ...... 14 1.6 Recent measurement of X-ray Polarization from astrophysical sources . 17 1.7 MeasuringX-rayPolarization . 21 1.8 Upcoming High energy polarization missions: . ..... 22 2 Description of the Instruments and Methods 25 2.1 Scientific Instruments Used for Data Analysis . ..... 25 2.1.1 AstroSat .............................. 26 2.1.1.1 LAXPC .......................... 27 2.1.2 XMM-Newton ............................ 29 2.1.2.1 EPICPN ......................... 29 2.1.3 RXTE ................................ 30 2.1.3.1 PCA............................ 32 2.1.4 Swift ................................. 32 xii Table of contents 2.1.4.1 BAT............................ 33 2.1.5 A Special Collimator with Flat Top Angular Response for POLIX. 34 2.1.6 Photo-electron Polarization Measurement Technique ....... 35 2.2 DataAnalysisMethods. 36 2.2.1 TimingAnalysis. .. .. .. 37 2.2.1.1 lcurve ........................... 37 2.2.1.2 powspec.......................... 37 2.2.1.3 efsearch .......................... 38 2.2.1.4 efold............................ 38 2.2.2 SpectralAnalysis . 38 2.2.2.1 Powerlaw with High Energy Cutoff Model . 39 2.2.2.2 Negative and Positive Powerlaw Exponential Model . 40 2.2.2.3 compTTModel. 40 2.2.2.4 Powerlaw with a Smoothed High Energy Cutoff (NEWH- CUT)Model ....................... 41 2.2.2.5 Powerlaw with a Fermi-Dirac Cutoff (FDCUT) Model 41 2.2.2.6 Gaussian Absorption Line Model . 41 2.2.2.7 Photoelectric Absorption Model . 42 2.2.2.8 GaussianLineProfile. 42 3 Pulse Phase Variation Of Cyclotron Resonance Absorption Feature 43 3.1 Effect Of High Magnetic Field On Accretion And High Energy Radiation 43 3.2 Formation Of CRSF And Variation In Its Parameters . .... 44 3.3 4U1907+09................................. 45 3.4 4U1538–522................................. 45 3.5 Observations................................. 46 3.6 DataAnalysis................................ 48 3.6.1 TimingAnalysis. .. .. .. 48 3.6.1.1 Timing Analysis Of 4U 1907+09 . 48 3.6.1.2 Timing Analysis Of 4U 1538–522 . 50 3.6.2 SpectralAnalysis . 53 3.6.2.1 Background Spectra And Response Matrix Files For SpectralAnalysis . 53 3.6.2.2 Models For Continuum Spectra . 53 3.6.2.3 Phase Average Spectrum Of 4U 1907+09 . 54 3.6.2.4 Phase Average Spectrum Of 4U 1538–522 . 56 3.6.2.5 Pulse Phase-Resolved Spectral Analysis Of 4U 1907+09 58 Table of contents xiii 3.6.2.6 Pulse Phase-Resolved Spectral Analysis Of 4U 1538–522 61 3.6.2.7 Intensity Resolved Spectral Analysis Of 4U 1907+09 . 63 3.7 DiscussionOnTheResults. 63 3.7.1 4U1907+09............................. 65 3.7.1.1 Energy Dependence Of The Pulse Profile And Period Evolution ......................... 65 3.7.1.2 The CRSF And A Possible Weak Luminosity Depen- dence ........................... 65 3.7.1.3 Pulse Phase Dependence Of The CRSF . 68 3.7.2 4U1538–522............................. 68 3.7.2.1 Long Term Increase In Cyclotron Line Energy . 68 3.7.2.2 Variation of Cyclotron Line Energy With Pulse Phase 69 3.7.2.3 The Emission Pattern of High Energy Radiation In ThisPulsar ........................ 70 3.8 Conclusions ................................. 70 3.8.1 4U1907+09............................. 70 3.8.2 4U1538–522............................. 71 4 Observations Of Some Isolated Neutron Stars 73 4.1 Introduction................................. 73 4.2 AstroSat Observations Of Rotation Powered Pulsar. 74 4.2.1 TheCrabNebula .......................... 75 4.2.2 PSRB1509–58 ........................... 76 4.2.3 Observations ............................ 77 4.2.4 TimingAnalysis. .. .. .. 77 4.2.5 SpectralAnalysis .
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