A Potential Progenitor for the Type Ic Supernova 2017ein

TL;DR

This paper reports the first identification of a credible progenitor system for a Type Ic supernova, SN 2017ein, using pre- and post-explosion imaging, and suggests it was likely a massive binary star system.

Contribution

The study provides the first direct detection and analysis of a progenitor system for a Type Ic supernova, including photometry and binary star modeling, advancing understanding of SN Ic origins.

Findings

Progenitor source is consistent with a massive binary system.

Progenitor's initial mass estimated at around 55 solar masses.

Best binary model involves an 80+48 solar mass system with a stripped star.

Abstract

We report the first detection of a credible progenitor system for a Type Ic supernova (SN Ic), SN 2017ein. We present spectra and photometry of the SN, finding it to be similar to carbon-rich, low-luminosity SNe Ic. Using a post-explosion Keck adaptive optics image, we precisely determine the position of SN 2017ein in pre-explosion \hst\ images, finding a single source coincident with the SN position. This source is marginally extended, and is consistent with being a stellar cluster. However, under the assumption that the emission of this source is dominated by a single point source, we perform point-spread function photometry, and correcting for line-of-sight reddening, we find it to have $M_{\rm F555W} = -7.5\pm0.2$ mag and $m_{\rm F555W}-m_{\rm F814W}$=$-0.67\pm0.14$ mag. This source is bluer than the main sequence and brighter than almost all Wolf-Rayet stars, however it is similar to some WC+O- and B-star binary systems. Under the assumption that the source is dominated by a single star, we find that it had an initial mass of $55\substack{+20-15} M_{\odot}$. We also examined binary star models to look for systems that match the overall photometry of the pre-explosion source and found that the best-fitting model is a $80$+$48 M_{\odot}$ close binary system in which the $80 M_{\odot}$ star is stripped and explodes as a lower mass star. Late-time photometry after the SN has faded will be necessary to cleanly separate the progenitor star emission from the additional coincident emission.