  The spatial and temporal coincidence of a GRB and a supernova explosion
(1998bw) on 25 April 1998 has raised conjectures on the physical connection
between the two phenomena, and in general on the association of GRBs with
supernovae, at least with the most powerful among them (hypernovae or
collapsars). In fact, multiwavelength observations of SN 1998bw have revealed
unusual characteristics: extremely high energy output at radio and optical
wavelengths, and relativistic expansion of the outgoing shock. The X-ray
emission of SN 1998bw, monitored by BeppoSAX starting ~10 hours after the GRB
detection, was remarkably prompt (within one day of supernova detonation), but
exhibited spectral and temporal properties similar to those of other supernovae
detected in X-rays.
