On the Lack of a Radio Afterglow from Some Gamma-ray Bursts - Insight into Their Progenitors?

TL;DR

This study compares gamma-ray bursts with and without radio afterglows, revealing differences in duration and circumburst environment that suggest distinct progenitor characteristics.

Contribution

It provides new insights into the physical conditions and progenitor models of GRBs by analyzing intrinsic properties related to radio afterglow presence.

Findings

Shorter intrinsic durations in bursts without radio afterglows

Differences in circumburst density profiles between the two groups

Weak correlation between energy and duration in no-radio group

Abstract

We investigate the intrinsic properties of a sample of bright (E_iso > 10^52 erg) gamma-ray bursts, comparing those with and without radio afterglows. We find that the sample of bursts with no radio afterglows has a significantly shorter mean intrinsic duration of the prompt gamma-ray radiation, and the distribution of this duration is significantly different from those bursts with a radio afterglow. Although the sample with no radio afterglow has on average lower isotropic energy, the lack of radio afterglow does not appear to be a result of simply energetics of the burst, but a reflection of a separate physical phenomenon likely related to the circumburst density profile. We also find a weak correlation between the isotropic gamma-ray energy and intrinsic duration in the sample with no radio afterglow, but not in the sample which have observed radio afterglows. We give possible explanations for why there may exist a sample of GRBs with no radio afterglow depending on whether the radio emission comes from the forward or reverse shock, and why these bursts appear to have intrinsically shorter prompt emission durations. We discuss how our results may have implications for progenitor models of GRBs.