A size-duration trend for gamma-ray burst progenitors

TL;DR

This paper investigates the relationship between emission region size and duration in gamma-ray bursts, revealing a size-duration trend that applies to both short and long GRBs, with characteristic sizes around 2 x 10^10 cm and 4 x 10^11 cm.

Contribution

It establishes a size-duration relation for GRB emission regions, providing new constraints on their physical scales during prompt emission.

Findings

Emission region size R ~ c x T_90 for both GRB types

Characteristic sizes are ~2 x 10^10 cm for short GRBs

Characteristic sizes are ~4 x 10^11 cm for long GRBs

Abstract

Gamma-ray bursts (GRBs) show a bimodal distribution of durations, separated at a duration of ~2 s. Observations have confirmed the association of long GRBs with the collapse of massive stars. The origin of short GRBs is still being explored. We examine constraints on the emission region size in short and long GRBs detected by Fermi/GBM. We find that the emission region size during the prompt emission, R, and the burst duration, T$_{90}$, are consistent with the relation R ~ c x T$_{90}$, for both long and short GRBs. We find the characteristic size for the prompt emission region to be ~2 x 10$^{10}$ cm, and ~4 x 10$^{11}$ cm for short and long GRBs, respectively.