Characterizing the Reflection Spectrum of MAXI J1803-298 with NuSTAR

MAXI J1803-298 is a transient black hole candidate that was discovered in May of 2021 by MAXI during an outburst that lasted several months. Multiple follow-up observations reveal recurring dipping intervals in several of the X-ray light curves of the source, particularly during the hard/hard intermediate states – typically with a recurring period of ~7 hrs. We report results from the analysis of the four NuSTAR observations of the source over the duration of the outburst evolution. Our reflection spectroscopy analysis reveals the black hole to be rapidly spinning with a viewing angle close to the plane of the disc. Additionally, we detect line features in some of the spectra including the narrow component of the iron K-shell emission complex, plausibly indicating significant contribution from distant reflection. Moreover, absorption lines at ~6.6 keV and ~6.9 keV are also detected, which coincide with the energies of the Fe XXV and Fe XXVI absorption lines, respectively. We posit that these signatures are caused by absorption due to an outflow or equatorial disc wind in the system passing over the line of sight to the central X-ray source.