SN 1998bw at late phases
  We present observations of the peculiar supernova SN 1998bw, which was probably associated with GRB 980425. The photometric and spectroscopic evolution is monitored up to 500 days past explosion. We also present modeling based on spherically symmetric, massive progenitor models and very energetic explosions. The models allow line identification and clearly show the importance of mixing. From the late light curves we estimate that about 0.3-0.9 solar masses of ejected Nickel-56 is required to power the supernova. 
Jesper Sollerman, Cecilia Kozma, Claes Fransson, Bruno Leibundgut,   Peter Lundqvist, Felix Ryde, and Patrick Woudt