GRB 040403: A faint X-ray rich gamma-ray burst discovered by INTEGRAL^*

¹ Istituto di Astrofisica Spaziale e Fisica Cosmica – CNR, Sezione di Milano “G.Occhialini”, via Bassini 15, 20133 Milano, Italy e-mail: sandro@mi.iasf.cnr.it
² Dipartimento di Fisica, Università degli Studi di Milano Bicocca, P.zza della Scienza 3, 20126 Milano, Italy
³ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁴ Instituto de Astrofísica de Andalucía (IAA-CSIC), Apartado de Correos 3004, 18080 Granada, Spain
⁵ Physics Department, University of Ferrara, via Paradiso 12, 44100 Ferrara, Italy
⁶ Istituto di Astrofisica Spaziale e Fisica Cosmica – CNR, Sezione di Bologna, via Gobetti 101, 40129 Bologna, Italy
⁷ Clemson University, Department of Physics & Astronomy, Clemson, SC 29634-0978, USA
⁸ Niels Bohr Institute, Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁹ Astronomical Institute, Academy of Sciences of the Czech Republic, 251 65 Ondrejov, Czech Republic
¹⁰ University of California at Berkeley, Space Sciences Laboratories, Berkeley, CA 94720-7450, USA
¹¹ Integral Science Data Centre, Chemin d'Écogia 16, 1290 Versoix, Switzerland
¹² Istituto di Astrofisica Spaziale e Fisica Cosmica – CNR, Sezione di Roma, via Fosso del Cavaliere 100, 00133 Roma, Italy

Received: 20 September 2004
Accepted: 1 December 2004

Abstract

GRB 040403 is one of the faintest gamma-ray bursts for which a rapid and accurate localization has been obtained. Here we report on the gamma-ray properties of this burst, based on observations with the IBIS instrument aboard INTEGRAL, and the results of searches for its optical afterglow. The steep spectrum (power law photon index = 1.9 in the 20–200 keV range) implies that GRB 040403 is most likely an X-ray rich burst. Our optical limit of R > 24.2 at 16.5 h after the burst, indicates a rather faint afterglow, similar to those seen in other relatively soft and faint bursts.