Spectral analysis of 35 GRBs/XRFs observed with HETE-2/FREGATE^*

¹ Laboratoire d'Astrophysique, Observatoire Midi-Pyrénées, 31400 Toulouse, France
² C.E.S.R., Observatoire Midi-Pyrénées, 31028 Toulouse Cedex, France
³ UC Berkeley Space Sciences Laboratory, Berkeley CA 94720-7450, USA
⁴ Center for Space Reserach, MIT, Cambridge, MA , USA
⁵ Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
⁶ Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
⁷ RIKEN (Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
⁸ Consiglio Nazionale delle Ricerche (IASF), via Piero Gobetti, 101-40129 Bologna, Italy
⁹ Department of Physics, Aoyama Gakuin University, Chitosedai 6-16-1 Setagaya-ku, Tokyo 157-8572, Japan
¹⁰ National Astronomical Observatory, Osawa 2-21-1, Mitaka, Tokyo 181-8588 Japan
¹¹ Los Alamos National Laboratory, PO Box 1663, Los Alamos, NM, 87545, USA
¹² Tsukuba Space Center, National Space Development Agency of Japan, Tsukuba, Ibaraki, 305-8505, Japan

Corresponding author: C. Barraud, barraud@ast.obs-mip.fr

Received: 21 June 2002
Accepted: 13 January 2003

Abstract

We present a spectral analysis of 35 GRBs detected with the HETE-2 gamma-ray detectors (the FREGATE instrument) in the energy range 7–400 keV. The GRB sample analyzed is made of GRBs localized with the Wide Field X-ray Monitor onboard HETE-2 or with the GRB Interplanetary Network. We derive the spectral parameters of the time-integrated spectra, and present the distribution of the low-energy photon index, alpha, and of the peak energy, . We then discuss the existence and nature of the recently discovered X-Ray Flashes and their relationship with classical GRBs.