# Observational evidence for mass ejection accompanying short gamma ray bursts

## TL;DR

The paper provides observational evidence for mass ejection in short gamma-ray bursts by identifying a short plateau in their duration distribution, supporting the hypothesis that these bursts originate from compact binary mergers involving ejecta.

## Contribution

It presents a new analysis of GRB duration data revealing a short plateau, consistent with jet crossing time through ejecta, supporting the merger origin of sGRBs.

## Key findings

- Detection of a ~0.4 sec plateau in short GRB durations
- Ejecta mass estimated to be a few percent of solar mass
- Supports merger model for short GRBs

## Abstract

The plateau in the duration distribution of long Gamma-Ray Bursts (LGRBs) provides a direct observational evidence for the Collapsar model. The plateau reflects the fact that the observed duration satisfies: $T_{90} = t_{e}-t_{b}$ where $t_{e}$ is the time that the central engine operates and $t_{b}$ is a threshold time, interpreted within the Collapsar model as the time it takes for the relativistic jet to penetrate the stellar envelope. Numerical simulation and macronova observations suggest that compact binary mergers involve mass ejection. If short-Gamma Ray Bursts (sGRBs) arise from such mergers, their jets should cross this surrounding ejecta before producing the prompt emission. Like in LGRBs, this should result in a distinct short plateau in the GRBs' duration distribution. We present a new analysis of the duration distribution for the three GRB satellites: BATSE, {\it Swift} and Fermi. We find a clear evidence for a short ($\sim 0.4$ sec) plateau in the duration distribution. This plateau is consistent with the expected jet crossing time, provided that the ejecta is of order of a few percent of solar masses.