Nucleosynthesis of56Ni in wind-driven supernova explosions and constraints on the central engine of gamma-ray bursts

Abstract

Theoretically expected natures of a supernova (SN) driven by a wind/jet are discussed. Approximate analytical formulations are derived to clarify basic physical processes involved in the wind/jet-driven explosions, and it is shown that the explosion properties are characterized by the energy injection rate (E iso ) and the mass injection rate (M iso ). To explain observations of Supernova 1998bw associated with gamma-ray burst (GRB) 980425, the following conditions are required: E iso M iso ≥ 10 51 erg M ⊙ s -2 and E iso ≥ 2 x 10 52 erg s -1 (if the wind Lorentz factor Γ w ∼ 1) or E iso ≥ 7 x 10 52 erg s -1 (if Γ w » 1). In Supernova 1998bw, 56 Ni (∼0.4 M ⊙ ) is probably produced in the shocked stellar mantle, not in the wind. The expected natures of SNe, e.g. ejected 56 Ni mass and ejecta mass, vary depending on E iso and M iso . The sequence of the SN properties from high E iso and M iso to low E iso and M iso is as follows: Supernova 1998bw-like - intermediate case - low mass ejecta (≤1 M ⊙ ) where 56 Ni is from the wind - whole collapse. This diversity may explain the diversity of SNe associated with GRBs. Our result can be used to constrain natures of the wind/jet, which are linked to the central engine of GRBs, by studying properties of the associated SNe.