THE FIRST <i>FERMI</i> -LAT GAMMA-RAY BURST CATALOG

TLDR

Over three years of Fermi‑LAT observations, high‑energy (>20 MeV) emission has been detected from 35 GRBs, and the collaboration’s analysis methodology is described. The catalog compiles these detections and systematically studies the temporal and spectral properties of LAT‑detected GRBs. The catalog was produced by analyzing 733 GBM‑triggered GRBs with a uniform LAT analysis sequence, and the study characterizes LAT emission’s delayed onset, extended duration, power‑law decay, and additional power‑law spectral component beyond the Band model. The catalog reports 28 GRBs detected above 100 MeV and 7 above ~20 MeV, and shows that LAT emission is delayed, longer, decays as a power law, and is dominated by a power‑law component in addition to the Band model.

Abstract

In three years of observations since the beginning of nominal science operations in August 2008, the Large Area Telescope (LAT) on board the Fermi Gamma Ray Space Telescope has observed high-energy (>20 MeV) \gamma-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above ~ 20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for GRB analysis are provided. We summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared to emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.