Early hard X-rays from the nearby core-collapse supernova SN2023ixf

We present NuSTAR observations of the nearby SN 2023ixf in M101 (d=6.9 Mpc) which provide the earliest hard X-ray detection of a non-relativistic stellar explosion to date at $\delta t\approx$4-d and $\delta t\approx$11-d. The spectra are well described by a hot thermal bremsstrahlung continuum with $T>25\mathrm{k}\mathrm{e}\mathrm{V}$ shining through a thick neutral medium with a neutral hydrogen column that decreases with time (initial $N_{\mathrm{H}\mathrm{i}\mathrm{n}\mathrm{t}}=2.6\times {10}^{23}\mathrm{c}{\mathrm{m}}^{-2}$). A prominent neutral Fe K$\alpha$ emission line is clearly detected, similar to other strongly interacting SNe such as SN2020jl. 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 $L_X\approx 2.5\times {10}^{40}$ 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 $n_{\mathrm{C}\mathrm{S}\mathrm{M}}\approx 4\times {10}^8\mathrm{c}{\mathrm{m}}^{-3}$ at $r<{10}^{15}\mathrm{c}\mathrm{m}$, corresponding to an enhanced progenitor mass-loss rate of $\dot{M}\approx 3\times {10}^{-4}$ M${}_{\odot }$ yr${}^{-1}$ for an assumed wind velocity of $v_w=50$ km s${}^{-1}$.