Astron. Astrophys. 347, L31-L34 (1999)

1. Introduction

The Gamma-Ray Burst Monitor (GBM) on board the X-ray satellite BSAX was triggered by a gamma-ray burst (GRB) on 29 March 1997, UT 3 h 44 m 30 s and localised by the Wide Field Camera (WFC) on BSAX at (uncertainty radius). GRB 980329 was very intense and reached a peak intensity of 6 Crab in the 2-26 keV range, being the second brightest burst localised so far with the WFCs (Frontera et al. 1998). The event was also detected by the burst and transient source experiment (BATSE) on board the Compton Gamma-Ray Observatory , which provided a position consistent with the one given by the WFC (Briggs et al. 1998). A follow-up observation was initiated within 7 hr with the BSAX narrow-field instruments (NFI). The observation revealed a previously unknown X-ray source, 1SAX J0702.6+3850, that faded by a factor of 3 over 14 hr of observation (int Zand et al. 1998). Radio observations performed with the VLA at 8.4 GHz resulted in the detection of a variable radio counterpart that peaked 3 days after the burst (Taylor et al. 1998a,b). This detection allowed observers to re-examine images taken on the first night after the gamma event. Thus, observations at the position of the radio counterpart revealed a fading source in the I- (Klose 1998), R- (Palazzi et al. 1998, Pedersen et al. 1998), and K-bands (Larkin et al. 1998a,b; Metzger 1998) as well as in submillimetre wavelengths (Smith & Tilanus 1998a,b).

The data provided by the Interplanetary Network (IPN) allowed to derive an annulus that intersected the WFC error and reduced its area (Hurley et al. 1998). The new error box included the 1SAX J0702.6+3850 X-ray source, the variable radio source and the optical transient (OT). Deep optical observations revealed a faint galaxy (R mag) coincident to the optical fading source (Djorgovski et al. 1998), that was pointed out as the GRB 980329 host galaxy. Here we present the result of the optical observations performed at several observatories.

© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999
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