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The Astrophysical Journal


The American Astronomical Society


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 phe-nomenological 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 $0.7. 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.