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 , SN 2017ein seems to have more prominent C II absorption and higher expansion velocities in early phases , suggestive of relatively lower ejecta mass .
The earliest photometry obtained for 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 .