An early peak in the radio light curve of short-duration Gamma-Ray Burst 200826A

TL;DR

This study reports early radio light curve observations of short-duration GRB 200826A, suggesting possible interpretations involving either a wind medium or a jet break, with implications for the burst's energy and geometry.

Contribution

First detailed radio and X-ray analysis of GRB 200826A, exploring early peak behavior and its implications for GRB environment and jet properties.

Findings

Radio light curve peaks around 4-5 days post-burst

Minimum equipartition energy estimated at ~3x10^47 erg

Jet opening angle estimated at 9-16 degrees

Abstract

We present the results of radio observations from the eMERLIN telescope combined with X-ray data from Swift for the short-duration Gamma-ray burst (GRB) 200826A, located at a redshift of 0.71. The radio light curve shows evidence of a sharp rise, a peak around 4-5 days post-burst, followed by a relatively steep decline. We provide two possible interpretations based on the time at which the light curve reached its peak. (1) If the light curve peaks earlier, the peak is produced by the synchrotron self-absorption frequency moving through the radio band, resulting from the forward shock propagating into a wind medium and (2) if the light curve peaks later, the turn over in the light curve is caused by a jet break. In the former case, we find a minimum equipartition energy of ~3x10^47 erg and bulk Lorentz factor of ~5, while in the latter case we estimate the jet opening angle of ~9-16 degrees. Due to the lack of data, it is impossible to determine which is the correct interpretation, however, due to its relative simplicity and consistency with other multi-wavelength observations which hint at the possibility that GRB 200826A is in fact a long GRB, we prefer scenario one over scenario two.