SN 2023ixf in Messier 101: A Variable Red Supergiant as the Progenitor Candidate to a Type II Supernova

We present preexplosion optical and infrared (IR) imaging at the site of the type II supernova (SN II) 2023ixf in Messier 101 at 6.9 Mpc. We astrometrically registered a ground-based image of SN 2023ixf to archival Hubble Space Telescope (HST), Spitzer Space Telescope (Spitzer), and ground-based near-IR images. A single point source is detected at a position consistent with the SN at wavelengths ranging from HST R band to Spitzer 4.5 mu m. Fitting with blackbody and red supergiant (RSG) spectral energy distributions (SEDs), we find that the source is anomalously cool with a significant mid-IR excess. We interpret this SED as reprocessed emission in a 8600 R-circle dot circumstellar shell of dusty material with a mass similar to 5 x 10(-5)M(circle dot) surrounding a log(L/L-circle dot) = 4.74 +/- 0.07 and T-eff 3920(-160)(+200) K RSG. This luminosity is consistent with RSG models of initial mass 11M(circle dot), depending on assumptions of rotation and overshooting. In addition, the counterpart was significantly variable in preexplosion Spitzer 3.6 and 4.5 mu m imaging, exhibiting similar to 70% variability in both bands correlated across 9 yr and 29 epochs of imaging. The variations appear to have a timescale of 2.8 yr, which is consistent with kappa-mechanism pulsations observed in RSGs, albeit with a much larger amplitude than RSGs such as alpha Orionis (Betelgeuse).