Timing variations in neutron stars: models, inference, and their implications for gravitational waves

Abstract

Timing variations in pulsars, low frequency ubiquitous structure known as timing noise and sudden increases in the rotational frequency which we call glitches, provide a means to study neutron stars. Since the first observations, many models have been proposed, yet no definitive explanation has arisen.

In this thesis, we aim to improve this situation by developing models of timing noise. We focus chiefly on precession models which explain periodic modulation seen in radio pulsar data. Developing models and testing them provides an opportunity to infer the elemental properties of neutron stars: evidence for long period precession has implications for the superfluid component predicted by models used to explain glitches. However, often more than one model can qualitatively explain the data, therefore we need a method to decide which model best fits the data. This is precisely the case for PSR B1828-11 which has been used as evidence for both precession and so-called magnetospheric switching. We address this confusion by applying the tools of probability theory to develop a Bayesian model comparison and find that the evidence is in favour of precession.

In the second part of this thesis, we will discuss the implications of timing variations for the detection of continuous gravitational waves from neutron stars. To search for these signals, matched filtering methods are used which require a template, a guess for what the signal ‘looks like’. Timing variations, as seen in the electromagnetic signal, may also exist in the gravitational wave signal. If detected, these could provide an invaluable source of information about neutron stars. However, if not included in the template, they may mean that the gravitational wave signal is not detected in the first place. We investigate this issue for both timing noise and glitches, using electromagnetic observations to predict for what types of gravitational wave searches this may be an issue. We find that while timing noise is unlikely to be an issue for current gravitational wave searches, glitches may cause a significant problem in all-sky searches for gravitational waves from neutron stars.

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Identifiers

ORCID for Ian Jones: orcid.org/0000-0002-0117-7567

ORCID for Nils Andersson: orcid.org/0000-0001-8550-3843

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