GAMMA-RAY BURST PROGENITORS CONFRONT OBSERVATIONS

The discovery of a supernova emerging at late times in the afterglow of GRB 030329 has apparently settled the issue on the nature of the progenitor of gamma-ray bursts. We now know that at least a fraction of cosmological GRBs are associated with the death of massive stars, and that the two explosions are most likely simultaneous. Even though the association was already suggested for GRB 980425, the peculiarity of that burst did not allow to extend the association to all GRBs. The issue is now to understand whether GRB 030329 is a "standard burst" or not. I will discuss some peculiarities of GRB 030329 and its afterglow lightcurve showing how, rather than a classical cosmological GRB, it looks more like a transition object linking weak events like GRB 980425 to the classical long duration GRBs. I will also discuss the problems faced by the Hypernova scenario to account for the X-ray features detected in several GRBs and their afterglows.