Spectral analysis of 50 GRBs detected by HETE-2

Abstract

FREGATE, the gamma-ray detector of HETE-2 is entirely dedicated to the study of GRBs. Its main characteristic is its broad energy range, from 7 keV to 400 keV. This energy range can be further extended down to 2 keV using the data from the WXM, the X-ray detector of HETE-2. Such a large energy range allows to study in details the prompt emission of GRBs, determining with a high precision their spectral parameters. Moreover, because this energy range extends at low energies, the sample of GRBs detected by both FREGATE and WXM contains a significant fraction of X-Ray Rich GRBs and X-Ray Flashes. We present here the distributions of the spectral parameters mesured for the time integrated spectra of 50 GRBs. We put emphasis on the distribution of the low energy spectral index alpha. Because FREGATE and WXM detected all classes of GRBs, we also discuss the connection between GRBs, X-Ray Rich GRBs and X-Ray Flashes.