A Systematic Analysis of Supernova Light in Gamma‐Ray Burst Afterglows

We systematically reanalyzed all Gamma-Ray Burst (GRB) afterglow datapublished through the end of 2002, in an attempt to detect the predictedsupernova light component and to gain statistical insight on itsphenomenological properties. We fit the observed photometric light curves asthe sum of an afterglow, an underlying host galaxy, and a supernova component.The latter is modeled using published multi-color light curves of SN 1998bw asa template. The total sample of afterglows with established redshifts contains21 bursts (GRB 970228 - GRB 021211). For nine of these GRBs a weak supernovaexcess (scaled to SN 1998bw) was found, what makes this to one of the firstsamples of high-z core collapse supernovae. Among this sample are all burstswith redshifts less than ~0.7. These results strongly support the notion thatin fact all afterglows of long-duration GRBs contain light from an associatedsupernova. A statistics of the physical parameters of these GRB-supernovaeshows that SN 1998bw was at the bright end of its class, while it was notspecial with respect to its light curve shape. Finally, we have searched for apotential correlation of the supernova luminosities with the properties of thecorresponding bursts and optical afterglows, but we have not found such arelation.Comment: 25 pages, 7 figures, accepted by ApJ; revised, shortened and updated compared to version 1; Title slightly changed; all figures showing individual afterglow light curves removed, as advised by the referee; conclusions unchange