Pulsar searching
Creators: name: Edwards, Russell T.
Publisher: name: Swinburne
Year: 2024

description: This thesis Research reports the results of two pulsar survey projects conducted at the Parkes 64-m radio telescope in New South Wales, Australia. The first, the Swinburne Intermediate Latitude Pulsar Survey, covered a large region of the southern Galaxy flanking that of the ongoing Galactic plane survey. We used the 13-feed 20 cm 'multibeam' receiver package to achieve this broad sky coverage in a short observing campaign with 14 days' total integration time. The survey proved remarkably successful, detecting 170 pulsars, 69 of which were new discoveries. Eight of the new discoveries possess small periods and period derivatives indicative of 'recycling', an hypothesis supported by the fact that six of them are in circular orbits with probable white dwarf companions. Pulse timing measurements have revealed that two of the white dwarfs are massive CO or ONeMg dwarfs. The mass of one of them (the companion to PSR J1157-5112) exceeds 1.14 M, providing the most convincing evidence to date for the production of 'ultra-massive' ONeMg white dwarfs as the end result of stellar evolution on the asymptotic giant branch (albeit with mass transfer indicated). PSR J1757-5322 also possesses a heavy white dwarf companion, in a close 11-h orbit. The proximity of the massive companion leads to significant relativistic orbital evolution and the effects of this will be measurable by pulsar timing in the coming decades. Under general relativity, the gravitational wave power radiated from the system is sufficient to cause coalescence in an event which will have dramatic and unknown consequences. Such events are possible gamma-ray burst sources, and the remnants could include isolated millisecond pulsars, close eclipsing binaries or pulsar planetary systems. The remaining four pulsar binaries show some discrepancies with the bulk of previously known low mass binary pulsars (LMBPs). PSR J1618-39 is in a 23-d orbit, filling what previously appeared to be a gap in the orbital period distribution. PSR J1745-0952 has a relatively long pulse period (19 ms) and along with PSR J1618-39 (12 ms) may have experienced a different evolutionary history to the majority of previously known LMBPs. A ninth pulsar discovered in the survey may also be recycled. The mean pulse profile of PSR J1411-7404 is exceedingly narrow and lies in stark contrast to that of other pulsars of similar pulse period. In the past the only other pulsars known with anomalously narrow profiles were believed (for other reasons) to have been recycled, and this fact in combination with the low period derivative measured in timing analysis of PSR J1411-7404 leads me to suggest that it, too, may have been recycled. If this is the case, it is possible that the recycling took place in a system similar in configuration to the progenitors of the double neutron star systems, but that sudden mass loss or an unfavourably oriented kick in the birth event of the second neutron star disrupted the system, leaving an isolated, mildly recycled pulsar. The second pulsar survey program conducted for this work was a targeted search of southern globular clusters. We used a baseband recording system to provide unprecedented time resolution (typically 25 μs). The large number of channels and short sampling interval achievable in software filterbanks, in combination with the ability to coherently remove most of the interstellar dispersion from clusters with previously known pulsars, made us the first to achieve a relatively flat sensitivity response to pulsars of ~10−3.5-10 s. This characteristic is vital if we are to constrain the true period distribution of millisecond pulsars, an important task in the evaluation of alternative equations of state for nuclear matter. We detected six millisecond pulsars and produced pulse profiles of higher resolution than were previously available. The basic sensitivity of the search was not high enough to detect any new pulsars, however the work demonstrates that the approach is feasible with the use of currently available high-performance computing resources (such as the Swinburne workstation cluster), and is capable of delivering excellent sensitivity characteristics. It is expected that future searches of this kind, of which this is the first, will achieve the goal of sampling the true pulse period distribution within a few years.