GRB observations by Fermi LAT revisited: new candidates found

TL;DR

This study revisits Fermi-LAT data to identify extended gamma-ray emissions associated with 581 known GRBs, discovering 19 bursts with high-energy signals, including four new detections, enhancing understanding of GRB high-energy behavior.

Contribution

The paper introduces a systematic search method for high-energy gamma-ray emission from GRBs using Fermi-LAT data, identifying four previously unreported high-energy GRB detections.

Findings

Detected high-energy emission in 19 GRBs.

Identified 4 new high-energy GRB candidates.

Extended gamma-ray emission observed up to 1500 seconds post-burst.

Abstract

We search the Fermi-LAT photon database for an extended gamma-ray emission which could be associated with any of the 581 previously detected gamma-ray bursts (GRBs) visible to the Fermi-LAT. For this purpose we compare the number of photons with energies E > 100 MeV and E > 1 GeV which arrived in the first 1500 seconds after the burst from the same region, to the expected background. We require that the expected number of false detections does not exceed 0.05 for the entire search and find the high-energy emission in 19 bursts, four of which (GRB 081009, GRB 090720B, GRB 100911 and GRB 100728A) were previously unreported. The first three are detected at energies above 100 MeV, while the last one shows a statistically significant signal only above 1 GeV.