Searching for Pulsars with the Effelsberg Telescope

Abstract

Pulsar searches have the potential to teach us much about the Universe in which we live. From the discovery of highly magnetised pulsars that enable detailed study of classical and quantum electrodynamics, to extremely stable, rapidly-rotating pulsars that will form integral parts of a timing array for the direct detection of gravitational waves, new pulsar discoveries are highly desirable.<br /> The high sensitivity of the Effelsberg telescope makes it one of the most powerful pulsar survey instruments in existence. Yet, despite this fact, the telescope has seen limited use by pulsar searchers. This thesis marks the beginning of a new era at Effelsberg, with 13 pulsars being discovered in this work, including two rapidly-rotating millisecond pulsars. These pulsars represent the first output from a new wave of pulsar surveys that use the state-of-the-art instrumentation at Effelsberg to observe the dynamic radio sky with unprecedented time and frequency resolution. <br /> To begin with, I present an introduction to pulsars, giving a brief overview of their observational characteristics and currently accepted evolutionary models (Chapter 1). I then go on to discuss the intricacies of performing a modern pulsar search. Here we review the techniques needed to go from a signal entering the receiver, to a pulsar discovery being made (Chapter 2). Having established the required knowledge base for the reader, I then present the methods and results of five diverse pulsar searches conducted as part of this work. <br /> The first of these surveys, deals with the hunt for radio-loud pulsars gamma-ray sources from the <i>Fermi</i> LAT First Source Catalog. Here, we have performed sensitive radio observations of 289 gamma-ray sources with no known association, leading to the discovery of the 2.65-ms pulsar J1745+1017. Through an extensive timing campaign involving three of Europe's largest radio telescopes, we have shown J1745+1017 to be a member of a new population of tight binary pulsars with very low-mass companions. Furthermore, through phase folding of the LAT gamma-ray photons, we conclusively show J1745+1017 to be a pulsed gamma-ray emitter. The high number of sources observed in this survey, make it the largest exploration of the LAT sky at radio frequencies (Chapter 3). <br /> The second survey presented, is the High Time Resolution Universe North pulsar survey (HTRU-North). This is an ambitious project to, in tandem with a partner survey using the Parkes radio telescope, perform an all-sky search for pulsars and fast transients. Here, we describe the strategy and sensitivity of our survey, and perform simulations of the expected discovery yield. This survey has already resulted in the discovery of 12 new pulsars, the timing parameters of which are presented. We close by discussing two of the survey's discoveries; PSR J1946+3414, a Galactic-disk millisecond pulsar in a highly-eccentric binary system, and PSR J2004+3427, a pulsar with a characteristic age of <19 kyr (Chapter 4). <br /> Finally, I describe targeted pulsar search observations of three objects of interest; 1RXS J141256.0+792204 (Calvera), an unidentified source of pulsed X-ray emission; SN 2008iz, a recent radio supernova in the M82 galaxy; and SGR 1833-0832, a recently discovered magnetar in outburst. No transient or periodic radio emission was detected from these sources. For each source, we discuss the implications of our non-detection and look at the possibilities for future observations (Chapter 5). <br /> I close the thesis by looking at what the future holds for pulsar searching.