Observations and Spectral Modelling of the Narrow-Lined Type Ic SN 2017ein

Abstract

SN 2017ein is a narrow-lined Type Ic SN that was found to share a location with a point-like source in the face on spiral galaxy NGC 3938 in pre-supernova images, making SN 2017ein the first credible detection of a Type Ic progenitor. Results in the literature suggest this point-like source is likely a massive progenitor of 60-80 M${}_{\odot }$, depending on if the source is a binary, a single star, or a compact cluster. Using new photometric and spectral data collected for 200 days, including several nebular spectra, we generate a consistent model covering the photospheric and nebular phase using a Monte Carlo radiation transport code. Photospheric phase modelling finds an ejected mass 1.2-2.0 M${}_{\odot }$ with an $E_{\mathrm{k}}$ of $\sim (0.9\pm 0.2)\times 10^{51}$ erg, with approximately 1 M${}_{\odot }$ of material below 5000 km s${}^{-1}$ found from the nebular spectra. Both photospheric and nebular phase modelling suggests a ${}^{56}$Ni mass of 0.08-0.1 M${}_{\odot }$. Modelling the [\OI] emission feature in the nebular spectra suggests the innermost ejecta is asymmetric. The modelling results favour a low mass progenitor of to 16-20 M${}_{\odot }$, which is in disagreement with the pre-supernova derived high mass progenitor. This contradiction is likely due to the pre-supernova source not representing the actual progenitor.

15 pages, 13 figures. Accepted for publication by MNRAS