Probing the low-luminosity gamma-ray burst population with new generation satellite detectors

Abstract

We compare the detection rates and redshift distributions of low-luminosity (LL) gamma-ray bursts (GRBs) localized by Swift with those expected to be observed by the new generation satellite detectors on the Gamma-ray Large Area Space Telescope (GLAST) (now Fermi) and, in future, the Energetic X-ray Imaging Survey Telescope (EXIST). Although the GLAST burst telescope will be less sensitive than Swift's in the 15-150 keV band, its large FoV implies that it will double Swift's detection rate of LL bursts. We show that Swift, GLAST and EXIST should detect about 1, 2 and 30 LL GRBs, respectively, over a 5-yr operational period. The burst telescope on EXIST should detect LL GRBs at a rate of more than an order of magnitude greater than that of Swift's BAT. We show that the detection horizon for LL GRBs will be extended from z ≃ 0.4 for Swift to z ≃ 1.1 in the EXIST era. Also, the contribution of LL bursts to the observed GRB redshift distribution will contribute to an identifiable feature in the distribution at z ≃ 1. © 2008 RAS.