The progenitor star of SN 2023ixf: A massive red supergiant with enhanced, Episodic Pre-Supernova mass loss

Abstract We identify the progenitor star of SN 2023ixf in Messier 101 using Keck/NIRC2 adaptive optics imaging and pre-explosion HST/ACS images. The supernova, localized with diffraction spikes and high-precision astrometry, unambiguously coincides with a progenitor candidate of mF814W = 24. 87 ± 0. 05 (AB). Given its reported infrared excess and semi-regular variability, we fit a time-dependent spectral energy distribution (SED) model of a dusty red supergiant (RSG) to a combined dataset of HST optical, ground-based near-infrared, and Spitzer/IRAC 3. 6, 4. 5 photometry. The progenitor resembles a RSG of Teff = 3488 ± 39 K and log (L/L⊙) = 5. 15 ± 0. 02, with a 0. 13 ± 0. 01 dex (31. 1 ± 1. 7 per cent) luminosity variation at a period of P = 1144. 7 ± 4. 8 days, obscured by a dusty envelope of τ = 2. 92 ± 0. 02 at 1 μm in optical depth (or AV = 8. 43 ± 0. 11 mag). The signatures match a post-main sequence star of 18. 2-₀. ₆^+1. 3\, M_ in Zero-Age Main Sequence mass, among the most massive SN II progenitor, with a pulsation-enhanced mass-loss rate of Ṁ= (4. 32 0. 26) 10^-4 \, M_ \, yr^-1. The dense and confined circumstellar material is ejected during the last episode of radial pulsation before the explosion. Notably, we find strong evidence for variations of τ or Teff along with luminosity, a necessary assumption to reproduce the wavelength-dependent variability, which implies periodic dust sublimation and condensation. Given the observed SED, partial dust obscuration remains possible, but any unobstructed binary companion over 5. 6 M⊙ can be ruled out.