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Pulsar Characteristics Across the Energy Spectrum

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Pulsar Characteristics Across the Energy Spectrum Pulsar Characteristics Across The Energy Spectrum Agnieszka Slo wikowska Nicolaus Copernicus Astronomical Center Department of Astrophysics in Torun´ Ph. D. Thesis written under the supervision of Dr. Bronis law Rudak Warsaw 2006 I dedicate this thesis to my husband Acknowledgements I am deeply grateful to many people for their help and support during my studies. In particular, I would like to thank Dr. Bronis law Rudak for giving me the opportunity to work as a member of a pulsar group at Copernicus Astronomical Center, and for supervising my PhD thesis. I am grateful to the Director of CAMK for offering me the fellowship, support, and excellent conditions to study and work. I am grateful to both, the European Association for Research in Astronomy Marie Curie Training Site and Deutsche Akademischer Austausch Dienst for the EARASTAR- GAL and DAAD fellowships, respectively. This work was also supported by KBN grant 2P03D.004.24. I am very grateful to Bronek Rudak for all his help, support and advice during my PhD. I would especially like to thank him for reading the thesis and for giving me comments and advice on how to significantly improve it. I appreciate very much his help in organising the formal preparation of getting the degree. I am thankful for financial support, for sending letters of recommendation, and for allowing me to present my work at various conferences and meetings. Additionally, for encouraging me to apply for different fellowships and for giving me opportunities to work outside Poland. I am most grateful for his friendship. I would like to thank Gottfried Kanbach, Axel Jessner, Lucien Kuiper, Wim Hermsen, Roberto Mignani and Werner Becker for giving me the possibilities to work with them. Special thanks to Gottfried Kanbach for his support during the application for the EARA and DAAD fellowships. Very deep thanks to Jarek Dyks for always being ready to explain and discuss theoretical pulsar aspects. Special thanks to Gottfried Kanbach, Axel Jessner and Roberto Mignani for writing recommendation letters. All my work could not have been done without help from Jurek Borkowski and Micha l Ja´stak. Thank you very much for being patient and `user- friendly' computer administrators. I am grateful to all people from CAMK administration department for being very helpful with all administrative procedures. I am thankful to all my astronomical and non-astronomical friends that I met in Poland, Holland and Germany, not only for astronomical discus- sions, but also for great time that I spent with them. Special thanks to all my Polish friends for a great time spent far away from the computer. I would like to thank my family, especially my husband Tomek for being so patient with me, for forgiving all my strange ideas and for his uncon- ditional love. I am grateful to my parents, Marek and Ela, for their love, support and help during my PhD: to my Daddy for pushing me with writ- ing the thesis, and to my Mom for designing and building our great house. Many thanks to my private doctors, my sis Iza and her's husband Adam. To Iza for taking care of my health, and to Adam and Dr. Brycki for the greatest surgic operation ever done. Thank you. 4 Contents 1 Introduction 1 1.1 Neutron stars and pulsars . 1 1.2 Observational characteristics of pulsars . 6 1.3 Distribution of pulsars in the Galaxy . 12 1.4 Pulsars across the electromagnetic spectrum . 12 1.5 The Crab pulsar and its nebula . 17 1.6 An outline of the thesis and statement of originality . 19 2 Enhanced radio emission from the Crab pulsar 21 2.1 Introduction . 21 2.2 Giant radio pulses . 26 2.3 Effelsberg observations . 26 2.3.1 EPOS - the Effelsberg Pulsar Observation System . 27 2.3.2 LeCroy oscilloscope - an ultra-high resolution detection system 28 2.4 EPOS data analysis . 28 2.4.1 GRPs statistics . 29 2.4.2 Polarisation . 32 2.5 High resolution detections . 35 2.6 Conclusions . 35 3 Optical polarimetry of the Crab pulsar 39 3.1 Introduction . 39 3.2 Observations . 40 3.2.1 Nordic Optical Telescope . 40 3.2.2 OPTIMA instrument . 41 3.2.3 Weather and seeing conditions during the observations . 47 3.3 Data reduction . 51 3.3.1 Flat field correction . 51 i CONTENTS 3.3.2 Raw data binning . 51 3.3.3 Rotating polarisation filter characteristics . 53 3.3.4 Polarisation data analysis . 62 3.3.5 The HST polarisation standards . 73 3.4 Results . 78 3.4.1 Nebular contribution . 78 3.4.2 Time alignment between optical and radio wavelengths . 82 3.4.3 Polarisation characteristics of the Crab pulsar . 84 3.4.4 Polarisation characteristics of the Crab pulsar after DC sub- traction . 89 3.5 Summary and discussion . 89 3.6 Conclusions . 97 4 PSR B0540-69 - the Crab twin in the Large Magellanic Cloud 98 4.1 Introduction . 98 4.2 The INTEGRAL satellite . 99 4.3 Observations . 100 4.4 IBIS/ISGRI data analysis and results . 102 4.5 JEM-X data analysis and results . 111 4.6 Summary . 115 5 PSR B1929+10 revisited in X-rays 116 5.1 Introduction . 116 5.2 Previous results . 117 5.3 Observations . 118 5.4 Timing analysis . 120 5.4.1 ROSAT PSPC-B . 120 5.4.2 ROSAT HRI . 122 5.4.3 ASCA GIS . 123 5.4.4 RXTE PCA . 125 5.5 Comparison of the X-ray and radio profile . 127 5.6 Spectral analysis . 128 5.6.1 High value of the neutral hydrogen column density . 131 5.7 The X-ray emitting trail . 133 5.8 Summary and conclusions . 134 6 Closing remarks 142 ii CONTENTS A OPTIMA data files 145 B ROSAT timing 147 iii Chapter 1 Introduction 1.1 Neutron stars and pulsars The discovery of pulsars In 1934 Baade and Zwicky suggested that stars might end their lives as neutron stars (Baade & Zwicky 1934a,b). This hypothesis was introduced in an effort to account for liberation of tremendous amount of energy in supernova explosions. They suggested the existence of stars and cores of stars with the average density of nuclear matter. It took more that 30 years to confirm the existence of these objects in the Universe. The first object (which eventually turned out to be a rapidly rotating highly magnetised neutron star) - CP 1919 - was discovered by Jocelyn Bell and Antony Hewish at Cambridge in 1967 (Hewish et al. 1968). The pulse period of 1.3373 s was much shorter than the time scale on which normal stars can vary, and the recurrence of the pulses was extremely regular. This object is known as PSR B1919+211 now. Radially pulsating white dwarf stars were proposed at first as an explanation and remained popular for some time (Hewish et al. 1968). In contrast to neutron stars, white dwarfs had been observed and relatively well understood for some time. This idea was even more supported when the second periodicity in the original pulsar, having the source in the drifting subpulses, was observed (Drake & Craft 1968). It was considered as higher harmonics of fundamental frequency. By the end of the year 1968 the situation changed dramatically. Two new pulsars were discovered: in the Vela supernova remnant a 0.089 s pulsar was found (Large et al. 1968), and the Crab Nebula turned out to host a 0.033 s pulsar (Staelin & Reifenstein 1968). These new 1PSR stands for Pulsating Source of Radio, while the numbers refer to its position at the sky, and the letter B refers to the coordinate system 1950. The modern convention is for all pulsars to have a J designation (2000 coordinates) and to retain the B designation only for those published prior to about 1993. 1 1. INTRODUCTION observations were not speaking in favour of the oscillating white dwarf hypothesis. The rapidity of the pulsation ruled out this hypothesis. Moreover, pulsars were linked clearly to supernovae now. Various phenomenological models of possible sources of these `pulsing' signals were proposed. One of them was a `neutron star lighthouse' model proposed by Gold (1968) and by Pacini (1967). Franco Pacini and Tommy Gold interpreted the repeating signals as the `lighthouse' effect. They concluded independently that the radio beams were being emitted by a rotating, highly magnetised neutron star. Strong magnetic fields and subluminal rotation speeds would lead to relativistic velocities in any plasma in the surrounding magnetosphere, leading to anisotropic radiation in the form of a rotating beacon. This explanation - in which the radio waves are produced by synchrotron radiation from relativistic particles that are accelerated by the star's magnetic field - was then positively verified. The discovery by Richards & Comella (1969) that the Crab pulsar is slowing down its rotation was a firm confirmation of a rotating neutron-star model. The measured slow-down rate could be well explained by a dipolar magnetic field, which had to be strong to power the Crab Nebula (Pacini 1967). The observed value of the slow-down and the moment of inertia of a neutron star implied an energy loss rate that closely matched the observed luminosity of the nebula. Evidently, energetic particles, fed by the rotational energy, were responsible for it (Gold 1969). The idea of neutron stars Neutron stars (NS) are compact objects with masses comparable to that of the Sun but compressed into a volume with radius of about 10 to 15 km. They are formed in supernova explosions as the result of gravitational core-collapse of a massive (with initial mass between 8M and 30M ) star.
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