Fermi Large Area Telescope observations of GRB 110625A

TL;DR

This paper reports Fermi LAT observations of GRB 110625A, revealing GeV emission with a complex light curve and discussing its possible origin as synchrotron self-Compton radiation from UV flares.

Contribution

First detailed GeV emission analysis of GRB 110625A, showing a complex light curve and proposing a new emission mechanism.

Findings

Detected GeV emission between 180s and 580s after burst

Identified two distinct emission periods in the GeV light curve

No X-ray flaring observed during GeV emission period

Abstract

Gamma-ray bursts (GRBs) that emit photons at GeV energies form a small but significant population of GRBs. However, the number of GRBs whose GeV-emitting period is simultaneously observed in X-rays remains small. We report gamma-ray observations of GRB 110625A using Fermi's Large Area Telescope (LAT) in the energy range 100 MeV to 20 GeV. Gamma-ray emission at these energies was clearly detected using data taken between 180s and 580s after the burst, an epoch after the prompt emission phase. The GeV light curve differs from a simple power-law decay, and probably consists of two emission periods. Simultaneous Swift/XRT observations did not show flaring behaviors as in the case of GRB 100728A. We discuss the possibility that the GeV emission is the synchrotron self-Compton radiation of underlying ultraviolet flares.