Faint high-energy gamma-ray photon emission of GRB 081006A from Fermi observations

TL;DR

This paper reports the detection and analysis of high-energy gamma-ray emission from GRB 081006A using Fermi observations, confirming its association with multiple high-energy photons and comparing its properties to other long-duration GRBs.

Contribution

The paper presents the first unambiguous detection of GRB 081006A via the matched filter technique and provides detailed temporal and spectral analysis of its high-energy emission.

Findings

GRB 081006A is associated with over 13 high-energy photons above 100 MeV.

The properties of GRB 081006A are similar to GRB 080825C, especially in late high-energy photon emission.

There is a notable scarcity of faint LAT-detected GRBs in the current sample.

Abstract

Since the launch of the Fermi gamma - ray Space Telescope on June 11, 2008, the LAT instrument has solidly detected more than 20 GRBs with high energy photon emission above 100 MeV. Using the matched filter technique, 3 more GRBs have also shown evidence of correlation with high energy photon emission as demonstrated by Akerlof et al. In this paper, we present another GRB unambiguously detected by the matched filter technique, GRB 081006A. This event is associated with more than 13 high energy photons above 100 MeV. The likelihood analysis code provided by the $Fermi$ Science Support Center (FSSC) generated an independent verification of this detection by comparison of the Test Statistics (TS) value with similar calculations for random LAT data fields. We have performed detailed temporal and spectral analysis of photons from 8 keV up to 0.8 GeV from the GBM and the LAT. The properties of GRB 081006A can be compared to the other two long duration GRBs detected at similar significance, GRB 080825C and GRB 090217A. We find that GRB 081006A is more similar to GRB 080825C with comparable appearances of late high energy photon emission. As demonstrated previously, there appears to be a surprising dearth of faint LAT GRBs, with only one additional GRB identified in a sample of 74 GRBs. In this unique period when both $Swift$ and $Fermi$ are operational, there is some urgency to explore this aspect of GRBs as fully as possible.