The peculiar Type Ia supernova iPTF14atg: Chandrasekhar-mass explosion or violent merger?

TL;DR

This study compares explosion models for different progenitors of the peculiar Type Ia supernova iPTF14atg, finding that a violent white dwarf merger best explains its spectral evolution, though the early UV flash remains unexplained.

Contribution

The paper demonstrates that a violent white dwarf merger model fits the spectral evolution of iPTF14atg better than single-degenerate models, challenging previous interpretations of its early UV flash.

Findings

Merger model matches spectral evolution from 10 days before to weeks after maximum light.

Single-degenerate models struggle to explain spectral evolution.

Early UV flash may be due to ejecta interaction or surface radioactivity.

Abstract

iPTF14atg, a subluminous peculiar Type Ia supernova (SN Ia) similar to SN 2002es, is the first SN Ia for which a strong UV flash was observed in the early-time light curves. This has been interpreted as evidence for a single-degenerate (SD) progenitor system where such a signal is expected from interactions between the SN ejecta and the non-degenerate companion star. Here, we compare synthetic observables of multi-dimensional state-of-the-art explosion models for different progenitor scenarios to the light curves and spectra of iPTF14atg. From our models, we have difficulties explaining the spectral evolution of iPTF14atg within the SD progenitor channel. In contrast, we find that a violent merger of two carbon-oxygen white dwarfs with 0.9 and 0.76 solar masses, respectively, provides an excellent match to the spectral evolution of iPTF14atg from 10d before to several weeks after maximum light. Our merger model does not naturally explain the initial UV flash of iPTF14atg. We discuss several possibilities like interactions of the SN ejecta with the circum-stellar medium and surface radioactivity from a He ignited merger that may be able to account for the early UV emission in violent merger models.