Searching for Needles in Haystacks - Using the Fermi/GBM to find GRB gamma-rays with the Fermi/LAT Detector

TL;DR

This paper presents a method using Fermi/LAT data to identify high-energy gamma-ray emissions from GRBs detected by Fermi/GBM, enhancing detection capabilities and potential for optical follow-up.

Contribution

It introduces a matched filter technique applied to LAT data to find high-energy GRB emissions that were previously undetected.

Findings

High confidence detection of high-energy emission for GRB 090228A.

Method improves identification of high-energy GRBs.

Potential for real-time detection and optical follow-up.

Abstract

From the launch of the Fermi Gamma-ray Space Telescope to July 9, 2010, the Gamma-ray Burst Monitor (GBM) has detected 497 probable GRB events. Twenty-two of these satisfy the simultaneous requirements of an estimated burst direction within 52^\circ of the Fermi Large Area Telescope (LAT) boresight and a low energy fluence exceeding 5 $\mu$erg/cm^2. Using matched filter techniques, the spatially correlated Fermi/LAT photon data above 100 MeV have been examined for evidence of bursts that have so far evaded detection at these energies. High energy emission is detected with great confidence for one event, GRB 090228A. Since the LAT has significantly better angular resolution than the GBM, real-time application of these methods could open the door to optical identification and richer characterization of a larger fraction of the relatively rare GRBs that include high energy emission.