SN 2023ixf in Messier 101: Photo-ionization of Dense, Close-in Circumstellar Material in a Nearby Type II Supernova

We present UV and/or optical observations and models of SN 2023ixf, a type II supernova (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 photoionization of dense, close-in circumstellar material (CSM) located around the progenitor star prior to shock breakout. These electron-scattering broadened line profiles persist for similar to 8 days with respect to first light, at which time Doppler broadened the features from the fastest SN ejecta form, suggesting a reduction in CSM density at r greater than or similar to 10(15) cm. The early time light curve of SN 2023ixf shows peak absolute magnitudes (e.g., M-u = -18.6 mag, M-g = -18.4 mag) that are greater than or similar to 2 mag brighter than typical type II SNe, 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 multiepoch 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) x 10(15) cm, and a progenitor mass-loss rate of M-center dot=10(-2 )M(circle dot) yr(-1). For the assumed progenitor wind velocity of v(w) = 50 km s(-1), this corresponds to enhanced mass loss (i.e., superwind phase) during the last similar to 3-6 yr before explosion.