SN 2004 aw : Confirming Diversity of Type Ic Supernovae ⋆

Optical and near-infrared (near-IR) observations of the Type Ic supernova (SN Ic) 2004aw are presented, obtained from −3 to +413 days with respect to the B-band maximum. The photometric evolution is characterised by a comparatively slow postmaximum decline of the light curves. The peaks in redder bands are significantly delayed relative to the bluer bands, the I-band maximum occurring 8.4 days later than that in B. With an absolute peak magnitude of −18.02 in the V band the SN can be considered fairly bright, but not exceptional. This also holds for the U -through-I bolometric light curve, where SN 2004aw has a position intermediate between SNe 2002ap and 1998bw. Spectroscopically SN 2004aw provides a link between a normal Type Ic supernova like SN 1994I and the group of broad-lined SNe Ic. The spectral evolution is rather slow, with a spectrum at day +64 being still predominantly photospheric. The shape of the nebular [O i] λλ6300, 6364 line indicates a highly aspherical explosion. Helium cannot be unambiguously identified in the spectra, even in the near-IR. Using an analytical description of the light-curve peak we find that the total mass of the ejecta in SN 2004aw is 3.5 – 8.0M⊙, significantly larger than in SN 1994I, although not as large as in SN 1998bw. The same model suggests that about 0.3M⊙ of Ni has been synthesised in the explosion. No connection to a GRB can be firmly established.