A NuSTAR and Swift View of the Hard State of MAXI J1813-095

Jiachen Jiang, Douglas J. K. Buisson, Thomas Dauser, Andrew C. Fabian, Felix Fürst, Luigi C. Gallo, Fiona A. Harrison, Michael L. Parker, James F. Steiner, John A. Tomsick, Santiago Ubach, Dominic J. Walton

Published 2022-05-17Version 1

We present an analysis of the NuSTAR and Swift spectra of the black hole candidate MAXI J1813-095 in a failed-transition outburst in 2018. The NuSTAR observations show evidence of reflected emission from the inner region of the accretion disc. By modelling the reflection component in the spectra, we find a disc inner radius of $R_{\rm in}<7$ $r_{\rm g}$. This result suggests that either a slightly truncated disc or a non-truncated disc forms at a few percent of the Eddington limit in MAXI J1813-095. Our best-fit reflection models indicate that the geometry of the innermost accretion remains consistent during the period of NuSTAR observations. The spectral variability of MAXI J1813-095 from multi-epoch observations is dominated by the variable photon index of the Comptonisation emission.