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From Millisecond Pulsars to Magnetars

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From Millisecond Pulsars to Magnetars ASearchforRadioPulsars: from Millisecond Pulsars to Magnetars Lina Levin Presented in fulfillment of the requirements of the degree of Doctor of Philosophy June 2012 Faculty of Information and Communication Technology Swinburne University i Abstract The southern High Time Resolution Universe (HTRU) survey for pulsars and fast transients is currently underway at the Parkes Radio Telescope in Australia. In this thesis we describe a search for pulsars in the intermediate latitude part (medlat) of this survey, which is now complete. With higher time and frequency resolution than previous surveys carried out in this region of the sky, the medlat survey was more sensitive to millisecond pulsars (MSPs) at higher distances from the Sun. We discuss the survey strategy and set up, the instrumentation used to collect data as well as the processing pipeline and search techniques used to discover pulsars in the data set. In total this survey has returned 104 newly discovered pulsars, including 26 MSPs. Some of these pulsars are particularly interesting, including an MSP with a Jupiter-mass companion, an eclipsing binary pulsar and an MSP suitable for the Pulsar Timing Array projects. A major find from the HTRU medlat survey was the radio magnetar PSR J1622–4950, which is described in detail in this thesis. Magnetars are slowly rotating neutron stars with extremely large surface magnetic field strengths, that occasionally undergo large outbursts of radiation. PSR J1622–4950 is one of 23 known magnetars and one of only 3 to have confirmed radio pulsations. The radio magnetars di↵er from ordinary rotation-powered pulsars e.g. by their highly variable flux densities, changing pulse profiles and flat radio spectrum. Evidence of a decrease by a factor of 2 over the last 700 days in the peak ⇠ flux density of PSR J1622–4950 is observed, indicating a transient nature. A fit of the rotating vector model to the position angle of the linear polarisation of the emission from the magnetar suggests a nearly aligned geometry of the pulsar. Finally, we have used the large number of MSPs discovered in the HTRU medlat survey to carry out a population study of MSPs in the Galaxy. Pulsar population studies make use of the observed properties of the known pulsar sample to derive the numbers and properties of the underlying Galactic population of pulsars. We have performed a large-scale flux-limited pulsar population synthesis study. At the derived best estimate of the scale height, z = 500 pc, the simulation implies an underlying population of 150,000 2 ⇠ MSPs with luminosities above L1400 = 0.07 mJy kpc . The results from the simulation predict that the two remaining parts of the southern HTRU survey will discover 85 ⇠ previously unknown MSPs. ii Acknowledgements The preparation and writing of this thesis has been an amazing journey, and many people have been a great help and support to me during my PhD. Firstly, I owe a huge thanks to my supervisors: Matthew Bailes, Simon Johnston, Willem van Straten and Michael Kramer. Thank you for teaching me about pulsars and astronomy, for pushing and encouraging me to always do better, but most of all for believing in me and my ability to become a good scientist and researcher. Matthew, thank you for taking the time to sit down with me and teach me all from ba- sic programming and scripting to complicated astronomy principles and instrumentation. Your contagious enthusiasm for pulsars and pulsar searching helped me make the decision to move across the world to do a PhD and I haven’t regretted it for a second. You have shared my excitement for every new discovery and good looking candidate - I am always going to hear your voice in my head shouting “Pulsar!” as a nice looking pdmp plot of a pulsar pops up on my screen. Simon, you have been a great support to me, especially during the last year. Our weekly meetings have helped me tremendously to get my work and ideas sorted, and to discuss any issue that has come up straight away. Thank you for pushing me to set deadlines and also for pushing me to keep them! Willem, your sense of detail and your ability to dig down to the bottom of every problem gives me faith in research. Thank you for teaching me the secrets of polarisation and the subtleties of the English language. Michael, thank you for inviting me to visit you in Bonn and for helping me with both survey and magnetar related issues. I am very grateful to have been part of the awesome pulsar gang at Swinburne: Matthew, Willem, Ramesh, Andrew, Jonathon, Sarah, Stefan, Paul and Ben. Thank you for always being around to help out with anything anytime it might come up or just for a co↵ee and a chat! I have also been very lucky to be backed up by the great HTRU team. Thank you all for sharing excitement over new discoveries, for finding pulsars, for confirming pulsars, for solving pulsars and for making long observing hours a lot easier. In particular, I would like to thank the people that I have worked closer together with: Mike (thank you for always helping me out with anything I needed, through countless numbers of emails with questions and discussions), Sam, Sabrina, Marta, Andrea, Ben and Cherry. Keep up the good work! To the wonderful sta↵ at Parkes, always happy to help out with any issue that might come up, observing related or not so observing related (such as driving to Forbes on a Friday night to pick up my missing bag, thanks again John!). Special thanks to Ettore Carretti, Brett Preisig and John Sarkissian. iii I have had great teachers and mentors also during the years leading up to the start of my PhD. I would like to thank Jan Ake˚ Nilsson, for believing I could do bigger and better things than I ever thought myself; P-O Fredriksson, for making me excited about physics and astronomy; Marek Abramowicz, for sharing your enthusiasm for research and for being committed to help me do well in my career. Thank you for helping me get to where I am today. My time in Australia has let me make amazing friends: Stefan, I am going to miss our random chats about everything from pulsars to giant woodpeckers (sometimes that step isn’t even very large!); Paul, thank you for co↵ee breaks and Friday chocolate and lunch at Grill’d, all with lots of chats and laughs; Sabrina, I am so glad you came to stay with me, you are a wonderful friend; Jono, thank you for taking care of me anytime I visited Sydney, and for all the card games! A special thank you also to Sarah and Max, Christina and Mike, Catarina, Ben, Evelyn, Emily, Caro and Frik, Vince, Chris, Francesco, Kathrin, Glenn, Anna, Adrian, Lee, Juan, Max, Carlos and all of the students at Swinburne. A huge thank you also to all of the Shooting Stars, I look forward to soccer nights all week! Sara, thank you for sharing my interest in astronomy and for always pushing me (or competing with me!) to do better. Those long hours of studying for physics exams in your kitchen, trying to resist the temptation of the deck of cards, seem to have paid o↵ for both of us! Helena and Kristofer, I know you are glad that I am happy where I am, but I still appreciate you making me feel missed by trying to find me any job you can in Sweden. Thank you all for being such lovely friends! Without the encouragement from my family at home, this work would have been a lot harder. Mamma and Pappa, thank you for supporting me in my decision to move to Australia to do my PhD, even if you hated the thought of me being so far away. Thank you also to Daniel and Frida, simply for being the best siblings in the world! Ian and Tricia, thank you for your warm welcome into your family and all the interest you show both in me and in what I do. Graeme, thank you for holding my hand both through the happy and the rough times. You are an amazing friend and I am happier than ever. This is only the beginning of the big adventure! Cheers everyone - I couldn’t have done it without you! iv v Statement of originality The work presented in this thesis has been carried out in the Centre for Astrophysics and Supercomputing at the Swinburne University of Technology (Hawthorn, VIC) and the Australia Telescope National Facility/CSIRO Astronomy and Space Sciences (Marsfield, NSW) between 2008 and 2012. During the last year, part of this work has been funded by the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020. This thesis contains no material that has been accepted for the award of any other degree or diploma. To the best of my knowledge, this thesis contains no material previously published or written by another author, except where due reference is made in the text of the thesis or included in this statement. The pulsar survey, on which the most of the work in this thesis is based, is a collabo- ration of a large number of researchers, initially comprised of the authors of Keith et al. (2010) and with another few scientists added during the course of the project. All mem- bers of the survey team have been contributing to the collection of data for the survey. I have personally visited the telescope >15 times during my PhD and spent more than 100 days observing.
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