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

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.

14 pages, 6 figures, MNRAS accepted

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• The Fourth Fermi-GBM Gamma-Ray Burst Catalog: A Decade of Data
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• On the $\alpha$-Intensity Correlation in Gamma-Ray Bursts: Subphotospheric Heating with Varying Entropy
• GRB 090510: a genuine short-GRB from a binary neutron star coalescing into a Kerr-Newman black hole
• The short gamma-ray burst population in a quasi-universal jet scenario
• A short gamma-ray burst from a proto-magnetar remnant
• Gamma Ray Burst studies with THESEUS