  We present UV/optical observations and models of supernova (SN) 2023ixf, a
type II SN located in Messier 101 at 6.9 Mpc. Early-time ("flash") spectroscopy
of SN 2023ixf, obtained primarily at Lick Observatory, reveals emission lines
of H I, He I/II, C IV, and N III/IV/V with a narrow core and broad, symmetric
wings arising from the photo-ionization of dense, close-in circumstellar
material (CSM) located around the progenitor star prior to shock breakout.
These electron-scattering broadened line profiles persist for $\sim$8 days with
respect to first light, at which time Doppler broadened features from the
fastest SN ejecta form, suggesting a reduction in CSM density at $r \gtrsim
10^{15}$ cm. The early-time light curve of SN2023ixf shows peak absolute
magnitudes (e.g., $M_{u} = -18.6$ mag, $M_{g} = -18.4$ mag) that are $\gtrsim
2$ mag brighter than typical type II supernovae, this photometric boost also
being consistent with the shock power supplied from CSM interaction. Comparison
of SN 2023ixf to a grid of light curve and multi-epoch spectral models from the
non-LTE radiative transfer code CMFGEN and the radiation-hydrodynamics code
HERACLES suggests dense, solar-metallicity, CSM confined to $r = (0.5-1) \times
10^{15}$ cm and a progenitor mass-loss rate of $\dot{M} = 10^{-2}$
M$_{\odot}$yr$^{-1}$. For the assumed progenitor wind velocity of $v_w = 50$ km
s$^{-1}$, this corresponds to enhanced mass-loss (i.e., ``super-wind'' phase)
during the last $\sim$3-6 years before explosion.
