Fermi observations of high-energy gamma-ray emission from GRB 090217A

TL;DR

This paper reports the detection and analysis of high-energy gamma-ray emission from GRB 090217A by the Fermi observatory, providing insights into its spectral and temporal properties and comparing it with previous LAT-detected bursts.

Contribution

It presents the first detailed high-energy analysis of GRB 090217A, highlighting differences from previous bursts and discussing implications for GRB emission models.

Findings

GRB 090217A was detected with >9 sigma significance by LAT.

Spectra are well fitted by a Band model across 8 keV to 1 GeV.

Unlike previous LAT GRBs, it shows no delayed high-energy onset.

Abstract

The Fermi observatory is advancing our knowledge of Gamma-Ray Bursts (GRBs) through pioneering observations at high energies, covering more than 7 decades in energy with the two on-board detectors, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Here we report on the observation of the long GRB 090217A which triggered the GBM and has been detected by the LAT with a significance greater than 9 sigma. We present the GBM and LAT observations and on-ground analyses, including the time-resolved spectra and the study of the temporal profile from 8 keV up to 1 GeV. All spectra are well reproduced by a Band model. We compare these observations to the first two LAT-detected, long bursts GRB 080825C and GRB 080916C. These bursts were found to have time-dependent spectra and exhibited a delayed onset of the high-energy emission, which are not observed in the case of GRB 090217A. We discuss some theoretical implications for the high-energy emission of GRBs.