Sn 2003lw and GRB 031203: A bright supernova for a faint gamma-ray burst

Optical and near-infrared observations of the gamma-ray burst GRB 031203, at z = 0.1055, are reported. A very faint afterglow is detected superposed onto the host galaxy in our first infrared JHK observations, carried out similar to 9 hr after the burst. Subsequently, a rebrightening is detected in all bands, peaking in the R band about 18 rest-frame days after the burst. The rebrightening closely resembles the light curve of a supernova like SN 1998bw, assuming that the GRB and the SN went off almost simultaneously, but with a somewhat slower evolution. Spectra taken close to the maximum of the rebrightening show extremely broad features as in SN 1998bw. The determination of the absolute magnitude of this SN ( SN 2003lw) is difficult owing to the large and uncertain extinction, but likely this event was brighter than SN 1998bw by 0.5 mag in the VRI bands, reaching an absolute magnitude. M-V = -19.75 +/- 0.15.