# Observations of SN 2017ein Reveal Shock Breakout Emission and A Massive Progenitor Star for a Type Ic Supernova

## TL;DR

This study presents detailed optical and UV observations of SN 2017ein, revealing shock breakout emission and identifying a massive progenitor star, likely a Wolf-Rayet star or a binary system, through pre-explosion HST imaging.

## Contribution

It provides the first detailed analysis linking early shock cooling signatures and progenitor properties for a Type Ic supernova using combined observational and modeling approaches.

## Key findings

- Shock cooling observed with an envelope mass of ~0.02 M$_{igodot}$ and radius of 8±4 R$_{igodot}$.
- Progenitor identified as a luminous, blue source consistent with a WR star or binary system.
- SN 2017ein shows higher early velocities and prominent CII absorption compared to typical SNe Ic.

## Abstract

We present optical and ultraviolet observations of nearby type Ic supernova SN 2017ein as well as detailed analysis of its progenitor properties from both the early-time observations and the prediscovery Hubble Space Telescope (HST) images. The optical light curves started from within one day to $\sim$275 days after explosion, and optical spectra range from $\sim$2 days to $\sim$90 days after explosion. Compared to other normal SNe Ic like SN 2007gr and SN 2013ge, \mbox{SN 2017ein} seems to have more prominent C{\footnotesize II} absorption and higher expansion velocities in early phases, suggestive of relatively lower ejecta mass. The earliest photometry obtained for \mbox{SN 2017ein} show indications of shock cooling. The best-fit obtained by including a shock cooling component gives an estimate of the envelope mass as $\sim$0.02 M$_{\odot}$ and stellar radius as 8$\pm$4 R$_{\odot}$. Examining the pre-explosion images taken with the HST WFPC2, we find that the SN position coincides with a luminous and blue point-like source, with an extinction-corrected absolute magnitude of M$_V$$\sim$$-$8.2 mag and M$_I$$\sim$$-$7.7 mag.Comparisons of the observations to the theoretical models indicate that the counterpart source was either a single WR star or a binary with whose members had high initial masses, or a young compact star cluster. To further distinguish between different scenarios requires revisiting the site of the progenitor with HST after the SN fades away.