Searching for extragalactic pulsars with MeerKAT

Abstract

Pulsars are rapidly rotating, highly magnetised neutron stars (NSs) that can be detected from the Earth via their radio pulses. The Small and Large Magellanic Clouds (SMC and LMC), two nearby dwarf satellites of the Milky Way, are the only galaxies outside our own in which radio pulsars have been discovered to date, hosting just 1 per cent of the radio pulsars known. The advent of the MeerKAT telescope in 2018, now the most sensitive radio telescope in the Southern Hemisphere, prompted fresh searches for faint or distant pulsars, notably extragalactic ones. Despite only a very small sample of pulsars outside our galaxy being known, the neutron star systems of the MCs have characteristics that are relatively rare in the Milky Way population, and are important to several branches of astrophysics. In particular, the SMC is a low-metallicity galaxy with recent and prolific star formation, that is expected to host a high density of young neutron stars, and pulsars in massive binary systems. Increasing the sample of extragalactic neutron stars will reveal the effect of the galactic environment on a NS population, and provide insights on high-mass stellar evolution and their final remnant properties. I performed a processing-intensive pulsar survey of the SMC as part of the TRAPUM (TRAnsients and PUlsars with MeerKAT) collaboration. I report the discovery of seven new SMC pulsars, doubling this galaxy's radio pulsar population and increasing the total extragalactic population by nearly a quarter. This survey also set strong upper limits on radio pulsations from a large variety of neutron star-related objects in the SMC, like the globular cluster NGC 121 and the rotation-powered X-ray pulsar J0058-7218. I then conducted timing observations (with the MeerKAT and Murriyang radio telescopes) of these SMC pulsars and two others previously discovered with Murriyang, over three years. This study increased the number of characterised extragalactic pulsars by 40 per cent; and revealed that two of the new pulsars, from which we detected giant glitches, are very 'young' and energetic radio pulsars powering pulsar wind nebulae. These are the first radio systems of their kind in the SMC and only one was previously known outside our galaxy. A third, somewhat older new pulsar was also seen to glitch. Finally, I report on a search of the more distant Sextans A and B galaxies which reduced the maximum luminosity limit for pulsars in these galaxies by a factor of 28, and yielded the serendipitous discovery of a background Fast Radio Burst which likely originated from a distant galaxy.

Date of Award	6 Jan 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Benjamin Stappers (Supervisor) & Lina Levin Preston (Supervisor)