Date of Graduation

2015

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Maura McLaughlin

Committee Co-Chair

Alan Bristow

Committee Member

Zachariah Etienne

Committee Member

Duncan Lorimer

Committee Member

D J Pisano

Abstract

Rotating radio transients (RRATs) are neutron stars are that characterized by the emission of strong sporadic bursts. We have analysed the long- and short-term time dependence of the pulse arrival times and the pulse detection rates for eight RRAT sources from the Parkes Multi-beam Pulsar Survey (PMPS). We find significant periodicities in the individual pulse arrival times from six RRATs. These periodicities range from ∼30 minutes to 2100 days and from one to 16 independent (i.e. non-harmonically related) periodicities are detected for each RRAT. In addition, we find that pulse emission is a random process on short (hour-long) time scales but that most of the objects exhibit longer term (months-years) non-random behaviour. We find that PSRs J1819--1458 and J1317--5759 emit more doublets (two consecutive pulses) and triplets (three consecutive pulses) than is expected in random pulse distributions. No evidence for such an excess is found for the other RRATs. There are several different models for RRAT emission depending on both extrinsic and intrinsic factors which are consistent with these properties.;Light travel time changes due to gravitational waves may be detected within the next decade through precision timing of an array of millisecond pulsars. Removal of frequency-dependent interstellar medium (ISM) delays due to dispersion and scattering is a key issue in the detection process. Current timing algorithms routinely correct pulse times of arrival (TOAs) for time-variable delays due to cold plasma dispersion. However, none of the major pulsar timing groups routinely correct for delays due to scattering from multi-path propagation in the ISM. Scattering introduces a phase change in the signal that results in pulse broadening and arrival time delays. As a step toward a more comprehensive ISM propagation delay correction, we demonstrate through a simulation that we can accurately recover pulse broadening functions (PBFs), such as those that would be introduced by multi-path scattering, with a realistic signal-to-noise ratio, with consequent improvements in timing precision. We also demonstrate that we can isolate the scattering delays from other types of delays, and show that reductions in the timing residual root-mean-square of more than a factor of two are possible through removal of time-variable scattering delays. We also show that the effect of pulse-to-pulse "jitter'' is not a serious problem for PBF reconstruction, at least for jitter levels comparable to those observed in several bright pulsars.

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