SN 2012ca: a stripped envelope core-collapse SN interacting with dense circumstellar medium

TL;DR

SN 2012ca, observed over a year, shows evidence of core-collapse origin rather than thermonuclear, due to spectral features indicating a Type Ic explosion interacting with dense circumstellar material.

Contribution

This study provides evidence that SN 2012ca is a core-collapse supernova, challenging previous thermonuclear interpretations for similar Type IIn-like events.

Findings

Spectral features indicate core-collapse origin.

SN 2012ca likely a Type Ic supernova.

Both thermonuclear and core-collapse channels may produce similar events.

Abstract

We report optical and near-infrared observations of SN 2012ca with the Public ESO Spectroscopy Survey of Transient Objects (PESSTO), spread over one year since discovery. The supernova (SN) bears many similarities to SN 1997cy and to other events classified as Type IIn but which have been suggested to have a thermonuclear origin with narrow hydrogen lines produced when the ejecta impact a hydrogen-rich circumstellar medium (CSM). Our analysis, especially in the nebular phase, reveals the presence of oxygen, magnesium and carbon features. This suggests a core collapse explanation for SN2012ca, in contrast to the thermonuclear interpretation proposed for some members of this group. We suggest that the data can be explained with a hydrogen and helium deficient SN ejecta (Type I) interacting with a hydrogen-rich CSM, but that the explosion was more likely a Type Ic core-collapse explosion than a Type Ia thermonuclear one. This suggests two channels (both thermonuclear and stripped envelope core-collapse) may be responsible for these SN 1997cy-like events.