GRB off-axis afterglows and the emission from the accompanying supernovae

TL;DR

This paper analyzes optical and radio afterglows of long-duration gamma-ray bursts viewed off-axis, comparing them with associated supernovae, and predicts detection prospects with upcoming radio surveys to better understand jet geometry and ejecta properties.

Contribution

It provides a detailed comparison of off-axis GRB afterglows with supernova emissions and suggests observational strategies for future radio surveys to detect these phenomena.

Findings

Few percent of off-axis optical afterglows are brighter than the SN

Observable optical off-axis afterglows occur within twice the jet's half-opening angle

Upcoming radio surveys can detect off-axis radio afterglows within a few hundred Mpc

Abstract

Gamma-ray burst (GRB) afterglows are likely produced in the shock that is driven as the GRB jet interacts with the external medium. Long-duration GRBs are also associated with powerful supernovae (SNe). We consider the optical and radio afterglows of long GRBs for both blasts viewed along the jet axis ("on-axis" afterglows) and misaligned observes ("off-axis" afterglows). Comparing the optical emission from the afterglow with that of the accompanying SN, using SN 1998bw as an archetype, we find that only a few percent of afterglows viewed off-axis are brighter than the SN. For observable optical off-axis afterglows, the viewing angle is at most twice the half-opening angle of the GRB jet. Radio off-axis afterglows should be detected with upcoming radio surveys within a few hundred Mpc. We propose that these surveys will act as "radio triggers", and that dedicated radio facilities should follow-up these sources. Follow-ups can unveil the presence of the radio SN remnant, if present. In addition, they can probe the presence of a mildly relativistic component, either associated with the GRB jet or the SN ejecta, expected in these sources.