Image-Plane Radio Transients on Short Timescales with ASKAP

Abstract

Short bursts, flares, scintillation, and other radio time-domain phenomena usually imply extreme astrophysical environments (e.g., strong magnetic fields). Therefore, these objects can be used as a laboratory to study extreme physics that cannot be studied on Earth. This time-domain parameter space, however, is relatively unexplored historically, mainly limited by instrumental sensitivity and field-of-view. In this thesis, I present results from untargeted radio transient surveys, focusing on short-timescales transients in the image plane. The surveys were conducted using new techniques with the ASKAP telescope. Firstly, I present the discovery of a group of rapidly scintillating galaxies arranged linearly on the sky and spanning approximately 2 degrees. This unlikely sky distribution reveals the existence of a nearby, straight, and high-pressured plasma filament, which produces extreme scintillation. More generally, I demonstrate the potential of identifying intra-observation transients (i.e., on the timescale of 15 min) from hours-long observations with ASKAP. This survey (using ASKAP pilot survey data) led to the discovery of 38 highly variable and transient sources, including pulsars, radio flaring stars, and extreme scintillators. Finally, I demonstrate the possibility of identifying new pulsars (especially unusual pulsars) in the image plane through their variable behaviours and polarisation. Based on this approach, I discovered a new, bright pulsar in the Large Magellanic Cloud. These discoveries have filled gaps in this poorly-explored time-domain parameter space. The presence of a nearby, high-pressured plasma filament also changes our understanding of the origins of extreme scintillation, and requires new models to explain the underlying phenomenon. Using the same technique we expect to discover ~1 highly variable source per day on the full ASKAP surveys.