Nucleosynthesis of 56Ni in wind-driven Supernova Explosions and Constraints on the Central Engine of Gamma-Ray Bursts
Abstract
Theoretically expected natures of a supernova 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 (Edotiso) and the mass injection rate (Mdotiso). To explain observations of SN 1998bw associated with Gamma-Ray Burst (GRB) 980425, the following conditions are required: Edotiso Mdotiso > ~ 1051 erg Msun s-2 and Edotiso > ~ 2 x 1052 erg s-1 (if the wind Lorentz factor Gammaw ~ 1) or Edotiso > ~ 7 x 1052 erg s-1 (if Gammaw >> 1). In SN 1998bw, 56Ni (~ 0.4Msun) is probably produced in the shocked stellar mantle, not in the wind. The expected natures of SNe, e.g., ejected 56Ni masses and ejecta masses, vary depending on Edotiso and Mdotiso. The sequence of the SN properties from high Edotiso and Mdotiso to low Edotiso and Mdotiso is the following: SN 1998bw-like -- intermediate case -- low mass ejecta (< ~ 1Msun$) where 56Ni is from the wind -- whole collapse. This diversity may explain the diversity of supernovae associated with GRBs. Our result can be used to constrain natures of the wind/jet, which is linked to the central engine of GRBs, by studying properties of the associated supernovae.