The nebular spectrum of the type Ia supernova 2003hv: evidence for a non-standard event

TL;DR

This study analyzes the nebular spectrum of supernova 2003hv, revealing that its features suggest a non-standard explosion likely involving a sub-Chandrasekhar mass white dwarf or a white dwarf merger, challenging classical models.

Contribution

It provides evidence that the inner ejecta mass of SN 2003hv is less than predicted by classical Chandrasekhar-mass models, supporting alternative explosion scenarios.

Findings

Classical W7 models cannot reproduce observed spectral features.

SN 2003hv likely resulted from a sub-Chandrasekhar mass explosion.

Inner ejecta mass is estimated to be around 0.5 solar masses.

Abstract

The optical and near-infrared late-time spectrum of the under-luminous Type Ia supernova 2003hv is analysed with a code that computes nebular emission from a supernova nebula. Synthetic spectra based on the classical explosion model W7 are unable to reproduce the large \FeIII/\FeII\ ratio and the low infrared flux at $\sim 1$ year after explosion, although the optical spectrum of SN\,2003hv is reproduced reasonably well for a supernova of luminosity intermediate between normal and subluminous (SN\,1991bg-like) ones. A possible solution is that the inner layers of the supernova ejecta ($v \lsim 8000$\,\kms) contain less mass than predicted by classical explosion models like W7. If this inner region contains $\sim 0.5 \Msun$ of material, as opposed to $\sim 0.9 \Msun$ in Chandrasekhar-mass models developed within the Single Degenerate scenario, the low density inhibits recombination, favouring the large \FeIII/\FeII\ ratio observed in the optical, and decreases the flux in the \FeII\ lines which dominate the IR spectrum. The most likely scenario may be an explosion of a sub-Chandrasekhar mass white dwarf. Alternatively, the violent/dynamical merger of two white dwarfs with combined mass exceeding the Chandrasekhar limit also shows a reduced inner density.