Gamma-ray burst predictions for the fermi gamma ray space telescope

Abstract

Results of a phenomenological model to estimate the gamma-ray burst (GRB) detection rate by the Fermi Gamma-Ray Space Telescope are reported. This estimate is based on the Burst and Transient Source Experiment (BATSE) 4B GRB fluence distribution, the mean ratio of fluences measured at 100 MeV-5 GeV with Energetic Gamma-Ray Experiment Telescope (EGRET) and at ≈20 keV-2 MeV with BATSE, and the mean EGRET GRB spectrum for the five EGRET spark-chamber GRBs. For a 10% fluence ratio and a number spectral index α1 = -2 at 100 MeV- 5 GeV energies, we estimate a rate of 20 and 4 GRBs yr-1 in the Fermi Large Area Telescope field of view (FOV) with at least five photons with energy E>100 MeV and E>1 GeV, respectively. We also estimate ≈1.5 GRBs yr-1 in the Fermi FOV where at least one photon with energy E>10 GeV is detected. For these parameters, we estimate ≈ 1-2 GRBs yr -1 detected with the Fermi telescope with more than 100 γ-rays with E ≳ 100 MeV. Comparison predictions for α1 = -2.2, different fluence ratios, and the AGILE γ-ray satellite are made. Searches for different classes of GRBs using a diagram plotting 100 MeV-10 GeV fluence versus 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. © 2009. The American Astronomical Society. All rights reserved..