Radio Transients with MeerKAT

Abstract

Radio astronomy is heading into a new era where we can use the wide field of view and excellent sensitivity of instruments such as LOFAR, the MWA, ASKAP, and MeerKAT to commensally search for and monitor radio variable and transient sources. In this thesis we present searches for, and investigations of, radio variable and transient sources in images from the “more” Karoo Array Telescope (MeerKAT). We describe the fast imaging pipeline for the more Transients and Pulsars (MeerTRAP) commensal search for fast radio transients and demonstrate its use on observations of the Vela pulsar. We will use the rapid imaging pipeline to localise the transients to determine their properties and to enable rapid follow-up with other instruments. We present the discovery and investigation of the first radio transient discovered with MeerKAT: MKT J170456.2-482100. This source was found commensally in ThunderKAT observations of the low-mass X-ray binary GX 339-4. We find that MKT J170456.2-482100 is an RS CVn-like stellar binary consisting of a K type sub-giant and companion of unknown type, and that the radio flares that we observe are likely due to magnetic activity of the K star. Further investigation is needed to determine the cause of faint features in the optical spectra and to determine the nature of the companion. We detect radio emission from X-ray flaring star EXO 040830-7134.7, the first radio star detected with MeerKAT. We find that this star is a magnetically active, rotating M-dwarf and that the radio emission we observe is likely caused by the magnetic activity. We investigate and present a solution to systematic flux density variability in the light curves of MeerKAT detected sources over time, though further investigation is required to determine the source of the systematics. Finally, we present the discovery of 25, 2.6 per cent of the radio sources in the field, new long-term variable sources in images made from two years of weekly monitoring observations of GX 339-4 with MeerKAT. This is an unprecedented data set, and the discoveries we present are only scratching the surface of what we can find out using these data. We present the radio light curves and spectral index variability of the new sources, and speculate on their nature. Many of the new variable sources are consistent with refractive scintillation of active galactic nuclei but other sources require further multi-wavelength studies to ascertain their nature. This thesis represents the new and exciting research into the radio variable sky that we can now perform using MeerKAT.

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Keith (Supervisor) & Benjamin Stappers (Supervisor)