On the light curves of stripped-envelope supernovae

Representative light curves of supernovae of Types Ib and Ic, and the peculiar Type II that makes a transition to Ib, are collected and analyzed. Their main characteristics are (1) a group of fast and heterogeneous light curves corresponding to spectroscopic Type Ic and (2) a group of intermediate and homogeneous light curves among which are examples of spectroscopic Types Ib, Ic, and II transition. The latter have a well-defined slope of similar to 0.019 mag day(-1) after similar to 150 days. A simple model based on the deposition of the energy provided by the radioactive decay of Ni-56 and Co-56 in expanding spherical shells is presented and used to qualitatively explain these families of light curves. The gamma-ray deposition function has two different regimes. At early times, it is strongly dependent on the physical parameters of the shells, which explains the heterogeneity of group 1 above. At late times, however, it reaches an asymptotic regime in which the slope in excess of the Co-56 decay rate is given by 5t(-1) log e mag day(-1), where t is the time since explosion in days, independently of any parameter of the ejecta. The photometric group 2 above may be, at least partially, a result of this asymptotic behavior.