Gamma Ray Burst Predictions for the Fermi Gamma Ray Space Telescope

TL;DR

This paper presents a phenomenological model to estimate the detection rate of gamma-ray bursts (GRBs) by the Fermi Gamma Ray Space Telescope, based on existing data and spectral assumptions, predicting several GRBs per year with high-energy photons.

Contribution

It introduces a new model to estimate GRB detection rates for Fermi based on BATSE and EGRET data, including spectral assumptions and comparison with other satellites.

Findings

Estimated ~20 GRBs per year with E > 100 MeV detected by Fermi.

Predicted ~4 GRBs per year with E > 1 GeV.

Forecasted ~1.5 GRBs per year with E > 10 GeV.

Abstract

Results of a phenomenological model to estimate the GRB detection rate by the Fermi Gamma ray Space Telescope are reported. This estimate is based on the BATSE 4B GRB fluence distribution, the mean ratio of fluences measured at 100 MeV - 5 GeV with EGRET and at 20 keV - 2 MeV with BATSE, and the mean EGRET GRB spectrum for the 5 EGRET spark-chamber GRBs. For a 10% fluence ratio and a number spectral index alpha_1 = -2 at 100 MeV - 5 GeV energies, we estimate a rate of ~ 20 and 4 GRBs per yr in the Fermi Large Area Telescope field of view with at least 5 photons with energy E > 100 MeV and E > 1 GeV, respectively. We also estimate ~ 1.5 GRBs per yr in the Fermi FoV where at least 1 photon with energy E > 10 GeV is detected. For these parameters, we estimate = 1 - 2 GRBs per year detected with the Fermi telescope with more than 100 gamma rays with E >~ 100$ MeV. Comparison predictions for alpha_1 = -2.2, different fluence ratios, and the AGILE gamma-ray satellite are made. Searches for different classes of GRBs using a diagram plotting 100 MeV - 10 GeV fluence vs. 20 keV - 20 MeV fluence is considered as a way to search for separate classes of GRBs and, specifically, spectral differences between the short-hard and long duration GRB classes, and for hard components in GRBs.