2023ApJ...952L...3G

We present NuSTAR observations of the nearby SN 2023ixf in M101 (d = 6.9 Mpc) that provide the earliest hard X-ray detection of a nonrelativistic stellar explosion to date at δt ≈ 4 days and δt ≈ 11 days. The spectra are well described by a hot thermal bremsstrahlung continuum with T > 25 keV shining through a thick neutral medium with a neutral hydrogen column that decreases with time (initial N_Hint = 2.6 × 10²³ cm^–2). A prominent neutral Fe Kα emission line is clearly detected, similar to other strongly interacting supernovae (SNe) such as SN 2010jl. The rapidly decreasing intrinsic absorption with time suggests the presence of a dense but confined circumstellar medium (CSM). The absorbed broadband X-ray luminosity (0.3-79 keV) is L_X ≈ 2.5 × 10⁴⁰ erg s^–1 during both epochs, with the increase in overall X-ray flux related to the decrease in the absorbing column. Interpreting these observations in the context of thermal bremsstrahlung radiation originating from the interaction of the SN shock with a dense medium we infer large particle densities in excess of n_CSM ≈ 4 × 10⁸ cm^–3 at r < 10¹⁵ cm, corresponding to an enhanced progenitor mass-loss rate of $\dot{M}\approx 3\times {10}^{-4}$M_⊙ yr^–1 for an assumed wind velocity of v_w = 50 km s^–1.