1 Introduction

In spite of the breakthrough obtained with BeppoSAX for the comprehension of the Gamma-Ray Burst (GRB) phenomenon, an exhaustive explanation is still lacking. Possible mechanisms have been conceived to explain GRBs, all of them involving compact objects and some suggesting an associated g.w. flux, although below the sensitivity of the presently operating g.w. detectors (Thorne 1992). However, due to the complete novelty of this phenomenon we consider certainly worthwhile to search whether a correlation between the GRBs and the data collected with g.w. detectors exists. The discovery of the supernova SN 1998bw, probably associated with the GRB 980425, prompted us to analyse the data of the Explorer detector around the time of GRB 980425. This unusual supernova was observed later (Galama et al. 1998) within the error box of GRB 980425 (Soffitta et al. 1998). The optical and radio light curves (Galama et al. 1998; Kulkarni et al. 1998b) imply that the supernova explosion probably occurred sometimes during the period 24-27 April 1998, consistent with the hypothesis that the SN 1998bw and the GRB 980425 occur simultaneously.