A Two‐Component Model for the Light Curves of Hypernovae

The light curves of 'hypernovae', i.e. very energetic supernovae with $E_{51}\equiv E/10^{51}$ergs $\gsim 5-10$ are characterized at epochs of a few monthsby a phase of linear decline. Classical, one-dimensional explosion models failto simultaneously reproduce the light curve near peak and at the linear declinephase. The evolution of these light curves may however be explained by a simplemodel consisting of two concentric components. The outer component isresponsible for the early part of the light curve and for the broad absorptionfeatures observed in the early spectra of hypernovae, similar to theone-dimensional models. In addition, a very dense inner component is added,which reproduces the linear decline phase in the observed magnitude-versus-timerelation for SNe 1998bw, 1997ef, and 2002ap. This simple approach does containone of the main features of jet-driven, asymmetric explosion models, namely thepresence of a dense core. Although the total masses and energies derived withthe two-component model are similar to those obtained in previous studies whichalso adopted spherical symmetry, this study suggests that the ejecta areaspherical, and thus the real energies and masses may deviate from thosederived assuming spherical symmetry. The supernovae which were modeled aredivided into two groups, according to the prominence of the inner component:the inner component of SN 1997ef is denser and more $^{56}$Ni-rich, relative tothe outer component, than the corresponding inner components of SNe 1998bw and2002ap. These latter objects have a similar inner-to-outer component ratio,although they have very different global values of mass and energy.Comment: To appear in the Astrophysical Journal, 2003, 593. 22 pages, including 4 figures and 3 table