X-ray Emission of Supernova 1998bw in the Error Box of GRB980425

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.