Contributed Talk - Splinter Relativistic

Friday, 25 September 2020, 10:20   (virtual room J)

Radio Afterglows of Very High Energy Gamma-Ray Bursts 190829A and 180720B

L. Rhodes; A. J. van der Horst; R. Fender; et al
Oxford/MPIfR Bonn; George Washington University; Oxford/Cape Town.

Ground-based Atmospheric Cherenkov Telescopes have now detected three very high energy counterparts to long Gamma-ray bursts (GRBs) at low redshifts: GRBs 190829A, 180720B and 190114C. In this talk, I will discuss the findings from Rhodes et al (2020) in which we present the results of a high cadence, multi-frequency radio observing campaign of GRB 190829A, along side complementary data from Swift XRT. We detected a probable forward shock component with both MeerKAT and XRT up to over 100 days post-burst. Conversely, the AMI-LA light curve appears to be dominated by reverse shock emission until around 70 days post-burst when the afterglow flux drops below the level of the host galaxy. We also present previously unpublished observations of the other H.E.S.S.-detected GRB, GRB 180720B, which shows possible forward shock emission that fades in less than 10 days. By comparing the radio afterglow emission of these two GRBs along with published GRB 190114C data, to a sensitivity-limited radio afterglow sample, we show that despite GRB 190829A having the lowest isotropic radio luminosity of any GRB in our sample, the distribution of luminosities is otherwise consistent. The very high energy GRBs are drawn from the same parent distribution as the other radio-detected long GRBs.