  SN 2017jgh is a type IIb supernova discovered by Pan-STARRS during the
C16/C17 campaigns of the Kepler/K2 mission. Here we present the Kepler/K2 and
ground based observations of SN 2017jgh, which captured the shock cooling of
the progenitor shock breakout with an unprecedented cadence. This event
presents a unique opportunity to investigate the progenitors of stripped
envelope supernovae. By fitting analytical models to the SN 2017jgh lightcurve,
we find that the progenitor of SN 2017jgh was likely a yellow supergiant with
an envelope radius of $\sim50-290~R_{\odot}$, and an envelope mass of
$\sim0-1.7~M_{\odot}$. SN 2017jgh likely had a shock velocity of
$\sim7500-10300$ km s$^{-1}$. Additionally, we use the lightcurve of SN 2017jgh
to investigate how early observations of the rise contribute to constraints on
progenitor models. Fitting just the ground based observations, we find an
envelope radius of $\sim50-330~R_{\odot}$, an envelope mass of
$\sim0.3-1.7~M_{\odot}$ and a shock velocity of $\sim9,000-15,000$ km s$^{-1}$.
Without the rise, the explosion time can not be well constrained which leads to
a systematic offset in the velocity parameter and larger uncertainties in the
mass and radius. Therefore, it is likely that progenitor property estimates
through these models may have larger systematic uncertainties than previously
calculated.
