Far-ultraviolet to Near-infrared Observations of SN 2023ixf: A High-energy Explosion Engulfed in Complex Circumstellar Material

We present early-phase panchromatic photometric and spectroscopic coverage spanning the far-ultraviolet to near-infrared regime of the nearest hydrogen-rich core-collapse supernova (SN) in the last 25 yr, SN 2023ixf. We observe early "flash" features in the optical spectra due to confined dense circumstellar material (CSM). We observe high-ionization absorption lines (Fe ii, Mg ii) in the ultraviolet spectra from very early on. We also observe a multipeaked emission profile of H alpha in the spectrum beginning at similar to 16 days, which indicates ongoing interaction of the SN ejecta with a preexisting shell-shaped CSM having an inner radius of similar to 75 au and an outer radius of similar to 140 au. The shell-shaped CSM is likely a result of enhanced mass loss similar to 35-65 yr before the explosion assuming a standard red supergiant wind. The UV spectra are dominated by multiple highly ionized narrow absorption and broad emission features from elements such as C, N, O, Si, Fe, and Ni. Based on early light-curve models of Type II SNe, we infer that the nearby dense CSM confined to 7 +/- 3 x 1014 cm (similar to 45 au) is a result of enhanced mass loss (10-3.0 +/- 0.5 M circle dot yr-1) two decades before the explosion.