Agile Detection of Delayed Gamma-Ray Emission from the Short Gamma-Ray Burst GRB 090510

TL;DR

This paper reports the first detection of delayed high-energy gamma-ray emission from a short gamma-ray burst, GRB 090510, revealing two distinct emission phases with different spectral properties and a power-law decay in the high-energy component.

Contribution

It presents the first observation of delayed gamma-ray emission in a short GRB, with detailed timing and spectral analysis, expanding understanding of short GRB emission mechanisms.

Findings

Detection of two emission phases in GRB 090510

Delayed gamma-ray emission above 30 MeV with a power-law decay

Distinct spectral properties between prompt and delayed phases

Abstract

Short gamma-ray bursts (GRBs), typically lasting less than 2 s, are a special class of GRBs of great interest. We report the detection by the AGILE satellite of the short GRB 090510 which shows two clearly distinct emission phases: a prompt phase lasting ~ 200 msec and a second phase lasting tens of seconds. The prompt phase is relatively intense in the 0.3-10 MeV range with a spectrum characterized by a large peak/cutoff energy near 3 MeV, in this phase, no significant high-energy gamma-ray emission is detected. At the end of the prompt phase, intense gamma-ray emission above 30 MeV is detected showing a power-law time decay of the flux of the type t^-1.3 and a broad-band spectrum remarkably different from that of the prompt phase. It extends from sub-MeV to hundreds of MeV energies with a photon index alpha ~ 1.5. GRB 090510 provides the first case of a short GRB with delayed gamma-ray emission. We present the timing and spectral data of GRB 090510 and briefly discuss its remarkable properties within the current models of gamma-ray emission of short GRBs.