published_or_final_version / abstract / Physics / Master / Master of Philosophy

This thesis 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 �s). 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.

The technique of pulsar timing reveals a wealth of new information when a precision of ∼1 μs or better is reached, but such precision is difficult to achieve. This thesis describes a series of very high precision timing observations that improve our knowledge of the targeted pulsar systems. We begin by describing a newly-developed baseband recording and coherent dedispersion system (CPSR2), along with a new object-oriented software development environment for pulsar data processing. Data obtained with this new instrument during a 3 year observing campaign at the Parkes 64m radio telescope are analysed in a number of novel ways. The mean profile of PSR J1022+1001 is shown to be stable on timescales of a few minutes, in contrast with previously published claims. We obtain a level of precision an order of magnitude better than any previous timing of this pulsar. In addition, we observe dramatic changes in the mean profile of the relativistic binary pulsar J1141?6545, which broadens by ∼50% over the time span of our observations. This is interpreted as evidence for secular evolution of the line of sight to the emission cone, caused by General relativistic geodetic precession which tilts the spin axis of the pulsar. High precision CPSR2 observations of the extraordinary double pulsar binary system are presented and we construct calibrated, mean polarimetric profiles for PSR J0737?3039A, in two frequency bands. These profiles provide a reference against which future profile evolution may be detected, given that we expect geodetic precession to alter the observed mean profile on an even shorter time scale than for PSR J1141?6545. The bulk of this thesis involves timing a selection of millisecond pulsars whose physical characteristics should allow the highest precision to be obtained. We measure several new proper motions and parallax distances. Shapiro delay is used to constrain the inclination angles and component masses of several of the binary systems in our source list. In addition, subtle periodic variations of the orbital parameters of two nearby binary millisecond pulsars are detected and attributed to annual orbital parallax, providing additional constraints on their three-dimensional orbital geometries. Future observations of these two sources may lead to more stringent tests of post-Keplerian gravitational theories. Finally, we use the timing residuals of one very stable source (PSR J1909?3744) as a reference against which we time PSR J1713+0747 with a root-mean-square precision of 133 ns, amongst the best timing residuals ever obtained. This result is an important step in the search for long-period gravitational waves using pulsar timing arrays.

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

As the successor of the Energetic Gamma Ray Experiment Telescope, the Large Area Telescope on board the Fermi Gamma-ray Space Telescope has measured the pulsations from over a hundred pulsars, a rapidly growing population in the gamma-ray sky. Pulsars spinning as fast as a few to ten milliseconds, the millisecond pulsars (MSPs), constitute over 30% of the population, with most of which found in binary systems. Many MSPs are found to have low-mass companions with masses less than ~ 0:1 of that of the Sun. Observations reveal that in these systems, the companion is irradiated by the radiation and/or the wind from the pulsar. It is believed that isolated MSPs in the Galactic field were once a member of such kind of systems, and have ablated their companion away. The gamma-ray emission from the original Black Widow pulsar was studied using data from the Fermi-LAT. The emission was found to depend on the orbital phase and an extra higher-energy component was observed near the inferior conjunction. The results can be explained by an inverse Compton (IC) process associated with the ultra-relativistic pulsar wind. PSR B1957+20 is the first black widow system from which evidence on interaction of unshocked pulsar wind is observed. In addition, diffuse X-rays were found from the globular cluster (GC) 47 Tucanae. It is believed that the observed gamma-rays and the diffuse X-rays can be produced via inverse Compton process between the background soft photons and the pulsar wind from the MSPs residing in the GC. The observation of diffuse X-rays from 47 Tucanae provides constraints on the energetics and the emission region for the IC scenario. They provide good examples and guides for search strategies of similar emissions in other black widow systems and globular clusters. / published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / abstract / toc / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

Proefschrift Universiteit van Amsterdam. / Op omslag: Puma. - Met bijdrage in het Nederlands. Met lit. opg.

Thesis (PhD) - Swinburne University of Technology, 2006. / A dissertation presented in fulfillment of the requirements for the degree of Doctor of Philosophy, Swinburne University of Technology - 2006. Typescript. Includes bibliographical references (p. 182-190).

Thesis (M. Phil.)--University of Hong Kong, 2008. / Also available online.