A high mass progenitor for the Type Ic Supernova 2007gr inferred from
  its environment
  We present an analysis of late-time Hubble Space Telescope Wide Field Camera
3 and Wide Field Planetary Camera 2 observations of the site of the Type Ic SN
2007gr in NGC 1058. The SN is barely recovered in the late-time WFPC2
observations, while a possible detection in the later WFC3 data is debatable.
These observations were used to conduct a multiwavelength study of the
surrounding stellar population. We fit spatial profiles to a nearby bright
source that was previously proposed to be a host cluster. We find that, rather
than being an extended cluster, it is consistent with a single point-like
object. Fitting stellar models to the observed spectral energy distribution of
this source, we conclude it is A1-A3 Yellow Supergiant, possibly corresponding
to a star with $M_{ZAMS} = 40M_{\odot}$. SN 2007gr is situated in a massive
star association, with diameter of $\approx 300\,\mathrm{pc}$. We present a
Bayesian scheme to determine the properties of the surrounding massive star
population, in conjunction with the Padova isochrones. We find that the stellar
population, as observed in either the WFC3 and WFPC2 observations, can be well
fit by two age distributions with mean ages: ~6.3 Myr and ~50 Myr. The stellar
population is clearly dominated by the younger age solution (by factors of 3.5
and 5.7 from the WFPC2 and WFC3 observations, respectively), which corresponds
to the lifetime of a star with $M_{ZAMS} \sim 30M_{\odot}$. This is strong
evidence in favour of the hypothesis that SN 2007gr arose from a massive
progenitor star, possibly capable of becoming a Wolf-Rayet star.
