Observational evidence for mass ejection accompanying short gamma ray bursts

Understand

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.