Type Ib supernova 2008D associated with the luminous X-ray transient 080109: An energetic explosion of a massive helium star

Abstract

We present a theoretical model for supernova SN 2008D associated with the luminous X-ray transient 080109. The bolometric light curve and optical spectra of the SN are modeled based on the progenitor models and the explosion models obtained from hydrodynamic/nucleosynthetic calculations. We find that SN 2008D is a more energetic explosion than normal core-collapse supernovae, with an ejecta mass of Mej = 5.3 ± 1.0M⊙ and a kinetic energy of EK = 6.0 ± 2.5 × 1051 erg. The progenitor star of the SN has a 6-8 M⊙ He core with essentially no H envelope (< 5 × 10-4M⊙) prior to the explosion. The main-sequence mass of the progenitor is estimated to be MMS = 20-25M⊙, with additional systematic uncertainties due to convection, mass loss, rotation, and binary effects. These properties are intermediate between those of normal SNe and hypernovae associated with gamma-ray bursts. The mass of the central remnant is estimated as 1.6-1.8 M⊙, which is near the boundary between neutron star and black hole formation.