DOI

https://doi.org/10.48717/djxv-fk09

Project

EG120

Title

High angular resolution imaging of a long lived GRB afterglow

Abstract

We propose to observe the radio counterpart of GRB171205A, the sixth closest gamma-ray burst detected (z=0.0368), whose afterglow is the second brightest at gigahertz frequencies and the the fourth longest-monitored (1500+ days post burst) to date. The very early X--optical--NIR emission is likely dominated by shock breakout emission while the supernova swamps the optical afterglow up to $\sim$50 days. Therefore late radio observations are the only key to unveil the jet properties. If the jet is observed slightly off-axis (as suggested by the observable cocoon shock breakout and corroborated by the GRB low luminosity) we should be able to measure the source proper motion. In this case radio observations would add a key parameter, namely the viewing angle, necessary to infer - for the first time in a long GRB - the jet-cocoon structure. Alternatively, a wide-angled jet with an intrisically low luminosity observed within its aperture cone should be resolved at the epoch of the proposed observations, thus providing unique insights into the jet dynamics. We will also submit a companion proposal to the LBA at the June deadline, in order to improve the resolution in north-south direction.