SN 2014C: a metamorphic supernova exploded in the intricate and hydrogen-rich surroundings

TL;DR

SN 2014C initially appeared as a typical Type Ib supernova but showed signs of hydrogen interaction early on, indicating complex circumstellar environment and additional energy sources beyond radioactive decay.

Contribution

This study provides detailed early observations of SN 2014C, revealing the presence of hydrogen and circumstellar interaction, which challenges the traditional classification of supernovae.

Findings

SN 2014C had a higher peak luminosity and faster rise than typical SNe Ib.

Presence of high-velocity hydrogen suggests a hydrogen-rich progenitor envelope.

Evidence of early interaction with circumstellar medium affecting the supernova's brightness evolution.

Abstract

We present photometric and spectroscopic observations of supernova (SN) 2014C, primarily emphasizing the initial month after the explosion at approximately daily intervals. During this time, it was classified as a Type Ib SN exhibiting a notably higher peak luminosity ($L_{\rm peak}\approx4.3\times10^{42}\rm erg\,s^{-1}$), a faster rise to brightness ($t_{\rm rise} \approx 11.6$ d), and a more gradual dimming ($\Delta m_{15}^{V} \approx 0.48$ mag) compared to typical SNe Ib. Analysis of the velocity evolution over the first $\sim$ 20 days after the explosion supports the view that the absorption near 6200\AA is due to high-velocity H$\alpha$ in the outer layers of the ejecta, indicating the presence of a small amount of hydrogen in the envelope of progenitor before the explosion. Assuming the peak luminosity is entirely attributed to radioactive decay, we estimate that 0.14 ${\rm M}_{\odot}$ of $^{56}$Ni was synthesized in the explosion. However, this amount of nickel could no longer maintain observed brightness approximately ten days after peak luminosity, suggesting additional energy sources beyond radioactive decay. This supplementary energy likely originates from interaction with the circumstellar medium (CSM). Consequently, the timing of the SN-CSM interaction in SN 2014C may occur much earlier than the emergence of IIn-like features during the nebular phase.