Speaker
Description
The excitement of the publicly announced 2019 TeV-detected GRBs motivated global multi-wavelength follow-up efforts, reinvigorated this field of transient astrophysics. Such detections have revealed the unexpected: TeV GRB emission may not be generated via synchrotron self-Comptonisation. While high-energy and optical follow-up of these TeV GRBs occurred within minutes of the discovery, most radio follow-up lagged behind by several days. In addition, much of the resulting modelling efforts have disregarded the radio spectrum entirely. However, very early-time radio detections of GRBs can directly probe the emitting population of electrons, the geometry, content and magnetic field structure of the outflows, the burst energetics, and the density structure of the pre-explosion environment. Such radio observations can disentangle other emission components from the forward shock, which is essential for understanding the TeV spectral shape. They will also help us to understand whether the structure of the circumburst medium effects the production of TeV photons. In collaboration with the HESS GRB team, we are triggering rapid and automated radio observations of HESS-detected GRBs using the Australia Telescope Compact Array (ATCA), providing the very earliest radio detections of these events. We have already successfully tested our triggering strategy on the long (TeV faint) GRB 210702A, detecting a rapidly evolving radio flare within 9-14 hrs post-burst. Such emission may arise from a thermally emitting population of electrons that were shock heated but not accelerated into a power law distribution. If this is the case, we would have made the first direct measurement of the fraction of electron accelerated in GRB shocks, providing further insight into the population involved in the TeV emission mechanisms. Such experiments are an excellent demonstration of the transient science that could be achieved via CTA and Square Kilometre Array synergies.
