The optical and infrared afterglow of GRB031203 and the associated hypernova SN 2003lw

Optical and near-infrared photometric observations of the host galaxy of GRB 031203 allowed us to detect a bump in its light curves, peaking about 18 rest-frame days after the burst. We interpreted this as due to the emergence of an associated SN. Subsequent spectroscopic observations allowed us to confirm the presence of a SN, named SN 2003lw. The presence of extremely broad features in these optical spectra, very similar to the ones seen in SN 1998bw, indicate that this is a very energetic hypernova. Moreover, it was even brighter than SN 1998bw. Therefore, the three best confirmed associations between a GRB (980425, 030329, 031203) and a SN involve hypernovae. However, while GRB030329 has properties “typical” of most GRBs, the other two are quite peculiar, in particular they are very weak and nearby. Thus, it is remarkable that the three hypernovae associated to these GRBs are so similar, while the GRBs themselves are very different. Thus, a lot of open questions still remain in the associations between SNe and long-duration GRBs, questions that will soon find an answer thanks to the launch of the Swift satellite.