Supernovae Shedding Light on Gamma-Ray Bursts

— We review the observational status of the Supernova (SN)/GammaRay Burst (GRB) connection. In section 2 we provide a short summary of the observational properties of core-collapse SNe. In sections 3-6 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. 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. In section 7, we provide an empirical estimate of the rate of Hypernovae, for a “MilkyWay-like” galaxy, of about ∼ 2.6×10 yr that may imply the ratio GRB/Hypernovae to be in the range ∼ 0.03−0.7. In the same framework we find the ratio GRB/SNe-Ibc to be ∼ 0.008÷0.05. In section 8 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. In section 9 we present the conclusions and highlight the open problems that Swift hopefully will allow us to solve.