MAXI J1803-298, a newly-discovered Galactic transient and black hole
candidate, was first detected by \emph{MAXI}/GSC on May 1st, 2021. In this
paper, we present a detailed spectral analysis of MAXI J1803-298. Utilizing the
X-ray reflection fitting method, we perform a joint fit to the spectra of MAXI
J1803-298, respectively, observed by \emph{NuSTAR} and \emph{NICER}/XTI on the
same day over the energy range between 0.7-79.0 keV, and found its spin (and
the inclination angle i) can be constrained to be close to an extreme value,
0.991 (i∼70∘), at 68\% confidence interval. The results suggest
that MAXI J1803-298 may be a fast-rotating black hole with a large inclination
angle.Comment: 6 pages, 5 figure