A two-component model for the light curves of hypernovae

The light curves of hypernovae, i.e., very energetic supernovae with E-51 = E/10(51) ergs greater than or similar to 5-10, are characterized by a phase of linear decline at epochs of a few months. Classical, one-dimensional explosion models fail to simultaneously reproduce the light curve near peak and at the linear decline phase. The evolution of these light curves may, however, be explained by a simple model consisting of two concentric components. The outer component is responsible for the early part of the light curve and for the broad absorption features observed in the early spectra of hypernovae, similar to the one-dimensional models. In addition, a very dense inner component is added, which reproduces the linear decline phase in the observed magnitude versus time relation for SN 1998bw, SN 1997ef, and SN 2002ap. This simple approach does contain one of the main features of jet-driven, asymmetric explosion models, namely, the presence of a dense core. Although the total masses and energies derived with the two-component model are similar to those obtained in previous studies that also adopted spherical symmetry, this study suggests that the ejecta are aspherical, and thus, the real energies and masses may deviate from those derived assuming spherical symmetry. The supernovae that were modeled are divided into two groups according to the prominence of the inner component: the inner component of SN 1997ef is denser and more Ni-56-rich, relative to the outer component, than the corresponding inner components of SN 1998bw and SN 2002ap. These latter objects have a similar inner-to-outer component ratio, although they have very different global values of mass and energy.