There is a short gamma-ray burst prompt phase at the beginning of each long one

TL;DR

This study shows that the initial prompt phase of long gamma-ray bursts shares spectral properties with short GRBs, implying a common emission mechanism and suggesting that short and long GRBs are fundamentally similar phenomena occurring on different timescales.

Contribution

It demonstrates that the early emission phase of long GRBs is spectrally similar to short GRBs, revealing a potential unified origin and emission process.

Findings

Short and early long GRBs follow the same E_p--E_iso correlation.

They are indistinguishable in the E_p--L_iso plane.

The initial phase of long GRBs is spectrally similar to short GRBs.

Abstract

We compare the prompt intrinsic spectral properties of a sample of short Gamma--ray Burst (GRB) with the first 0.3 seconds (rest frame) of long GRBs observed by Fermi/GBM. We find that short GRBs and the first part of long GRBs lie on the same E_p--E_iso correlation, that is parallel to the relation for the time averaged spectra of long GRBs. Moreover, they are indistinguishable in the E_p--L_iso plane. This suggests that the emission mechanism is the same for short and for the beginning of long events, and both short and long GRBs are very similar phenomena, occurring on different timescales. If the central engine of a long GRB would stop after ~0.3 * (1+z) seconds the resulting event would be spectrally indistinguishable from a short GRB.