A systematic analysis of supernova light in gamma-ray burst afterglows

We systematically reanalyzed all gamma-ray burst (GRB) afterglow data published through the end of 2002 in an attempt to detect the predicted supernova light component and to gain statistical insight into its phenomenological properties. We fit the observed photometric light curves as the sum of an afterglow, an underlying host galaxy, and a supernova component. The latter is modeled using published multicolor light curves of SN 1998bw as a template. The total sample of afterglows with established redshifts contains 21 bursts (GRB 970228 - GRB 021211). For nine of these GRBs a weak supernova excess ( scaled to SN 1998bw) was found, which is what makes this one of the first samples of high-z core-collapse supernovae. Among this sample are all bursts with redshifts less than similar to0.7. These results strongly support the notion that in fact all afterglows of long-duration GRBs contain light from an associated supernova. A statistics of the physical parameters of these GRB-supernovae shows that SN 1998bw was at the bright end of its class, while it was not special with respect to its light-curve shape. Finally, we have searched for a potential correlation of the supernova luminosities with the properties of the corresponding bursts and optical afterglows, but we have not found such a relation.