Early Hard X-Rays from the Nearby Core-collapse Supernova SN 2023ixf

Abstract

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 δ t ≈ 4 days and δ t ≈ 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 × 10 ^23 cm ^−2 ). A prominent neutral Fe K α 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 × 10 ^40 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 × 10 ^8 cm ^−3 at r < 10 ^15 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 .

Keywords

• Core-collapse supernovae