GRB 030406 – an extremely hard burst outside of the INTEGRAL field of view

¹ Space Research Center, Bartycka 18a, 00716 Warsaw, Poland e-mail: radek@cbk.waw.pl
² IPJ, 05-400 Swierk/Otwock, Poland
³ Astronomical Observatory, Warsaw University, Aleje Ujazdowskie 4, 00478 Warsaw, Poland
⁴ Nicolaus Copernicus Astronomical Center, Bartycka 18, 00716 Warsaw, Poland
⁵ SAp CEA, 91911 Gif-sur-Yvette, France
⁶ UMR 7164, 11 place M. Berthelot, 75231 Paris, France
⁷ Max-Planck Institute for extraterrestrial Physics, Giessenbachstrasse, 85748 Garching, Germany
⁸ Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA

Received: 8 August 2005
Accepted: 5 January 2006

Abstract

Using the IBIS Compton mode, the INTEGRAL satellite is able to detect and localize bright and hard GRBs, which happen outside of the nominal INTEGRAL field of view. We have developed a method of analyzing such INTEGRAL data to obtain the burst location and spectra. We present the results for the case of GRB 030406. The burst is localized with the Compton events, and the location is consistent with the previous Interplanetary Network position. A spectral analysis is possible by detailed modeling of the detector response for such a far off-axis source with an offset of 36.9 °. The average spectrum of the burst is extremely hard: the photon index above 400 keV is -1.7, with no evidence of a break up to 1.1 MeV at a 90% confidence level.