Pulsar searching and timing with the Parkes telescope

Abstract

Pulsars are highly magnetised, rapidly rotating neutron stars that radiate a beam of coherent radio emission from their magnetic poles. An introduction to the pulsar phenomenology is presented in Chapter 1 of this thesis. The extreme conditions found in and around such compact objects make pulsars fantastic natural laboratories, as their strong gravitational fields provide exclusive insights to a rich variety of fundamental physics and astronomy. <br /> The discovery of pulsars is therefore a gateway to new science. An overview of the standard pulsar searching technique is described in Chapter 2, as well as a discussion on notable pulsar searching efforts undertaken thus far with various telescopes. The High Time Resolution Universe (HTRU) Pulsar Survey conducted with the 64-m Parkes radio telescope in Australia forms the bulk of this PhD. In particular, the author has led the search effort of the HTRU low-latitude Galactic plane project part which is introduced in Chapter 3. We discuss the computational challenges arising from the processing of the petabyte-sized survey data. Two new radio interference mitigation techniques are introduced, as well as a partially-coherent segmented acceleration search algorithm which aims to increase our chances of discovering highly-relativistic short-orbit binary systems, covering a parameter space including the potential pulsar-black hole binaries. We show that under a linear acceleration approximation, a ratio of ~0.1 of data length over orbital period results <br /> in the highest effectiveness for this search algorithm.<br /> Chapter 4 presents the initial results from the HTRU low-latitude Galactic plane survey. From the 37 per cent of data processed thus far, we have re-detected 348 previously known pulsars and discovered a further 47 pulsars. Two of which are fast-spinning pulsars with periods less than 30 ms. PSR J1101-6424 is a millisecond pulsar (MSP) with a heavy white dwarf companion while its short spin period of 5 ms indicates contradictory full-recycling. PSR J1757-27 is likely to be an isolated pulsar with an unexpectedly long spin period of 17 ms. In addition, PSR J1847-0427 is likely to be an aligned rotator, and PSR J1759-24 exhibits transient emission property. We compare this newly-discovered pulsar population to that previously known, and we suggest that our current pulsar detection yield is as <br /> expected from population synthesis.<br /> The discovery of pulsars is just a first step and, in fact, the most interesting science can usually only be revealed when a follow-up timing campaign is carried out. Chapter 5 focuses on the timing of 16 MSPs discovered by the HTRU. We reveal new observational parameters such as five proper motion measurements and significant temporal dispersion measure variations in PSR J1017-7156. We discuss the case of PSR J1801-3210, which shows no significant period derivative after four years of timing data. Our best-fit solution shows a period derivative of the order of 10 to the power -23, an extremely small number compared to that of a typical MSP. However, it is likely that the pulsar lies beyond the Galactic Centre, and an unremarkable intrinsic period derivative is reduced to close to zero by the Galactic potential acceleration. Furthermore, we highlight the potential to employ PSR J1801-3210 in the strong equivalence principle test due to its wide and circular orbit. In a broader comparison with the known MSP population, we suggest a correlation between higher mass functions and the presence of eclipses in 'very low-mass binary pulsars', implying that eclipses are observed in systems with high orbital inclinations. We also suggest that the distribution of the total mass of binary systems is inversely-related to the Galactic height distribution. We report on the first detection of PSRs J1543-5149 and J1811-2404 as gamma-ray pulsars. <br /> Further discussion and conclusions arise from the pulsar searching and timing efforts conducted with the HTRU survey can be found in Chapter 6. Finally, this thesis is closed with a consideration of future work. We examine the prospects of continuing data processing and follow-up timing of discoveries from the HTRU Galactic plane survey. We also suggest potential improvements in the search algorithms aiming at increasing pulsar detectability.