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A Spectral Analysis of the Polarisation of Drifting Sub-Pulses

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Thesis(69.14 MB)

Date

2023

Authors

Supervisor

van Straten, Willem
Gulyaev, Sergei

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Thesis

Degree name

Master of Science (Research)

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Auckland University of Technology

Abstract

Pulsars are among the most extreme objects in the Universe. Each one is born during a supernova – a dramatic explosion that happens when a bright star many times bigger than our Sun runs out of fuel. The heavy core of the star collapses under its own weight into something more dense than the nucleus of an atom. Each pulsar has an inferred magnetic field that is millions of times stronger than any that can be produced here on the Earth. Like a cosmic lighthouse, this magnetic field generates beams that sweep across the Galaxy with each rotation of the star (Gold, 1968; Pacini, 1968); however, the underlying physics of the pulsar emission mechanism remains poorly understood after decades of study (Melrose & Yuen, 2016). Unlike the steady beam of a lighthouse, a pulsar’s beam crackles and pops with lightning-like discharges of energy (Ruderman & Sutherland, 1975). By studying this highly dynamic signal, we learn about what generates the radio waves and what happens as they travel through the turbulent plasma in the pulsar’s strong magnetic field. A relatively rare number of pulsars exhibit quasi-periodic variations in the polarisation state of their emission (e.g. Primak et al., 2022). To provide new insight into the origin of this behaviour, we developed a novel statistical method, based on Principal Component Analysis of the Fourier Transforms of the Stokes parameters, that extends the work of Edwards (2004) such that it can be applied in the case of quasi-periodic polarisation fluctuations. We apply this technique to the first-discovered pulsar, compare and contrast the results with previous work, and present the first detection of quasiperiodic drift frequency modulation. The method can be applied to a wide range of radio pulsars in order to obtain a quantitative measure of the fraction of pulsars that exhibit quasi-periodic polarisation fluctuations. In doing so, the techniques developed for this research project will provide new experimental constraints on theories of radio emission and propagation in the pulsar magnetosphere, and facilitate a deeper understanding of the physics of relativistic plasmas in strong magnetic fields.

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http://hdl.handle.net/10292/17517

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