Tests of the Kerr Hypothesis with MAXI J1803-298 Using Different RELXILL_NK Flavors

Iron line spectroscopy has been one of the leading methods not only for measuring the spins of accreting black holes but also for testing fundamental physics. Basing on such a method, we present an analysis of a dataset observed simultaneously by NuSTAR and NICER for the black hole binary candidate MAXI J1803-298, which shows prominent relativistic reflection features. Various relxill_nk flavors are utilized to test the Kerr black hole hypothesis. The results obtained from our analysis provide stringent constraints on Johannsen deformation parameter $\alpha_{13}$ with the highest precise to date, namely $\alpha_{13}=0.023^{+0.071}_{-0.038}$ from relxillD_nk and $\alpha_{13}=0.006^{+0.045}_{-0.022}$ from relxillion_nk respectively in 3-$\sigma$ credible lever, where Johannsen metric reduces to Kerr metric when $\alpha_{13}$ vanishes. Furthermore, we investigate the best model-fit results using Akaike Information Criterion and assess its systematic uncertainties.