A search for radio afterglows from gamma-ray bursts with the Australian Square Kilometre Array Pathfinder [article]

James K. Leung, Tara Murphy, Giancarlo Ghirlanda, David L. Kaplan, Emil Lenc, Dougal Dobie, Julie Banfield, Catherine Hale, Aidan Hotan, David McConnell, Vanessa A. Moss, Joshua Pritchard (+3 others)
2021 arXiv   pre-print
We present a search for radio afterglows from long gamma-ray bursts using the Australian Square Kilometre Array Pathfinder (ASKAP). Our search used the Rapid ASKAP Continuum Survey, covering the entire celestial sphere south of declination +41^∘, and three epochs of the Variables and Slow Transients Pilot Survey (Phase 1), covering ∼ 5,000 square degrees per epoch. The observations we used from these surveys spanned a nine-month period from 2019 April 21 to 2020 January 11. We crossmatched
more » ... sources found in these surveys with 779 well-localised (to ≤ 15") long gamma-ray bursts occurring after 2004 and determined whether the associations were more likely afterglow- or host-related through the analysis of optical images. In our search, we detected one radio afterglow candidate associated with GRB 171205A, a local low-luminosity gamma-ray burst with a supernova counterpart SN 2017iuk, in an ASKAP observation 511 days post-burst. We confirmed this detection with further observations of the radio afterglow using the Australia Telescope Compact Array at 859 days and 884 days post-burst. Combining this data with archival data from early-time radio observations, we showed the evolution of the radio spectral energy distribution alone could reveal clear signatures of a wind-like circumburst medium for the burst. Finally, we derived semi-analytical estimates for the microphysical shock parameters of the burst: electron power-law index p = 2.84, normalised wind-density parameter A_* = 3, fractional energy in electrons ϵ_e = 0.3, and fractional energy in magnetic fields ϵ_B = 0.0002.
arXiv:2102.01948v1 fatcat:tsdnnbeqlrberc33je7wad3cnm