Supernovae shedding light on gamma-ray bursts

We review the observational status of the Supernova (SN)/GammaRay Burst (GRB) connection. We review the circumstantial evidences and the direct observations that support the existence of a deep connection between the death of massive stars and GRBs. The present data suggest that SNe associated with GRBs form a heterogeneous class of objects including both bright and faint Hypernovae and perhaps also "standard" Ib/c events. We provide an empirical estimate of the rate of Hypernovae, for a "MilkyWay-like" galaxy, of about similar to 2.6 x 10(-4) yr(-1) that may imply the ratio GRB/Hypernovae to be in the range similar to 0.03-0.7. In the same framework we find the ratio GRB/SNe-Ibc to be similar to 0.008 divided by 0.05. We discuss the possible existence of a lag between the SN explosion and the associated gamma-ray event. In the few SN/GRB associations so far discovered the SN explosions and GRB events appear to go off simultaneously. Finally we present the conclusions and highlight the open problems that Swift hopefully will allow us to solve.