Examining ecliptic pulsars using the low frequency array telescope

Pulsars are rapidly rotating neutron stars with extreme magnetic fields, emitting beams of radio waves along their magnetic axes which is, in general, misaligned with their rotation axes. As these beams sweep across our line of sight, we observe periodic radio pulses allowing pulsars to serve as highly precise cosmic clocks. This property underpins the technique of pulsar timing, which enables a wide range of astrophysical investigations, from probing the interior structure of neutron stars to detecting low-frequency gravitational waves. In this thesis, we focus on a special group of pulsars, those that pass close to the Sun in the sky during part of the year, known as ecliptic pulsars. As their radio beams travel through the solar wind (a stream of charged particles flowing outward from the Sun), we see a change in their signals, resulting in measurable increases in dispersion measure (DM). We develop and apply a Bayesian framework that models the solar wind’s spatial electron density as a spherically symmetric distribution and its temporal variations as a power law in the power spectrum. This model effectively captures the dynamic nature of the solar wind and represents a promising approach for future pulsar timing array (PTA) noise modelling. Building on this modelling work, we launched a dedicated observational campaign targeting seven ecliptic pulsars using the Irish LOFAR (I-LOFAR) telescope, two of which are PTA sources. We applied high-precision pulsar timing techniques to derive accurate DM time series and investigated phenomena such as pulse nulling, frequency-dependent profile evolution, and DM chromaticity. Our results demonstrate the viability of using stand-alone LOFAR stations for high-fidelity low-frequency pulsar timing, a crucial asset for the European PTA and the broader low-frequency radio astronomy community. In the final component of this thesis, we explored the variable emission behaviour of an ecliptic source, PSR~B0656+14, a pulsar that exhibits features similar to rotating radio transients (RRATs). Using I-LOFAR observations, we conducted detailed statistical analyses including flux density distribution fitting, wait time studies, and single-pulse spectral index measurements to characterise its stochastic emission. We find compelling evidence for a memoryless emission process and a hybrid flux distribution, shedding new light on emission characteristics of RRAT-like pulsars. Together, these studies contribute not only to improving our understanding of solar wind effects on pulsar timing but also to the broader efforts of enhancing PTA sensitivity and using pulsars as precise probes of astrophysical plasmas. They also highlight the scientific potential of low-frequency radio observations from stand-alone LOFAR stations, both for solar wind studies and the characterisation of complex emission behaviours in pulsars.

Funder

College of Science and Engineering

Publisher

University of Galway

Rights

CC BY-NC-ND

cbn

Collections

University of Galway Theses (PhD Theses)