Seven Years of SN 2014C: a Multi-Wavelength Synthesis of an Extraordinary Supernova

TL;DR

This paper presents a comprehensive multi-wavelength analysis of supernova SN 2014C over seven years, revealing complex ejecta interactions, shock velocities, and a possible toroidal hydrogen structure around the progenitor.

Contribution

It provides new long-term optical spectroscopic data and a synthesis of multi-wavelength observations, proposing a novel toroidal hydrogen structure and detailed shock dynamics for SN 2014C.

Findings

Hα emission velocity width remains nearly constant at ~2000 km/s.

Radio data indicate a fast shock (~10,000 km/s) in rarified matter.

Infrared flux likely from a toroidal hydrogen structure.

Abstract

SN 2014C was originally classified as a Type Ib supernova, but at phase {\phi} = 127 d post-explosion strong H{\alpha} emission was observed. SN 2014C has since been observed in radio, infrared, optical and X-ray bands. Here we present new optical spectroscopic and photometric data spanning {\phi} = 947 - 2494 d post-explosion. We address the evolution of the broadened H{\alpha} emission line, as well as broad [O III] emission and other lines. We also conduct a parallel analysis of all publicly available multi-wavelength data. From our spectra, we find a nearly constant H{\alpha} FWHM velocity width of {\sim}2000 km/s that is significantly lower than that of other broadened atomic transitions ({\sim}3000 - 7000 km/s) present in our spectra ([O I] {\lambda}6300; [O III] {\lambda}{\lambda}4959,5007; He I {\lambda}7065; [Ca II] {\lambda}{\lambda}7291,7324). The late radio data demand a fast forward shock ({\sim}10,000 km/s at {\phi} = 1700 d) in rarified matter that contrasts with the modest velocity of the H{\alpha}. We propose that the infrared flux originates from a toroidal-like structure of hydrogen surrounding the progenitor system, while later emission at other wavelengths (radio, X-ray) likely originates predominantly from the reverse shock in the ejecta and the forward shock in the quasi-spherical progenitor He wind. We propose that the H{\alpha} emission arises in the boundary layer between the ejecta and torus. We also consider the possible roles of a pulsar and a binary companion.