Yuanming Wang (U Syd)

Yuanming Wang colloquium: Image-plane radio transients on minutes-timescales with ASKAP

Marsfield

Abstract

Short bursts, flares, scintillation and other radio time-domain phenomena usually imply extreme astrophysical environments (e.g. strong magnetic fields) that are difficult to achieve on Earth. This time-domain parameter space, however, is relatively unexplored historically, mainly limited by instrumental sensitivity and field-of-view (FoV). In this talk I will present unusual time-domain transient events I have discovered with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, including extreme scintillation, flaring stars, and pulsars.
We have used ASKAP to probe timescales of seconds to hours, searching for rapidly varying radio sources. With the advantage of the large FoV, we discovered a group of fast-scintillating galaxies arranged linearly on the sky, spanning approximately 2 degrees. Using this unlikely sky distribution we inferred the presence of a nearby, straight, and high-pressured plasma filament between the Earth and those galaxies, which produces extreme scintillation. Circular polarisation is another poorly explored parameter-space. With ASKAP dual-polarisation beams, we identified a new pulsar (rapidly rotating neutron star) PSR J0523-7125 through its strong circularly polarised emission and variable behaviour. PSR J0523-7125 shows many unusual properties (e.g., upturn spectrum shape), which may shed light on the as-yet-unknown pulsar coherent emission mechanism.
Our discovery has filled gaps in this unexplored time-domain parameter space, and highlighted a new way of finding unusual pulsars – useful for future space-time experiments. The existence 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, as existing theoretical models are incompatible with the structure we measured.