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We report results on the joint-fit of the NuSTAR and HXMT data for the blackhole X-ray binary candidate MAXI J1535-571. The observations were obtained in2017 when the source evolved through the hard, hard-intermediate andsoft-intermediate states over the rising phase of the outburst. Aftersubtracting continuum components, X-ray reflection signatures are clearlyshowed in those observations. By modeling the relativistic reflection indetail, we find that the inner radius $R_{\rm{in}}$ is relatively stable with$R_{\rm{in}}\lesssim 1.55 R_{\rm{g}}$ during the three states, which impliesthat the inner radius likely extends to the innermost stable circular orbiteven in the bright hard state. When adopting $R_{\rm{in}} = R_{\rm{ISCO}}$, thespin parameter is constrained to be $0.985_{-0.004}^{+0.002}$ at 90% confidence(statistical only). The best-fitting results reveal that the inclination of theinner accretion disc is $\sim70-74$ degrees, which notably conflicts with theapparent orientation of the ballistic jet ($\leqslant$45 degrees). In addition,both the photon index and the electron temperature increase during thetransition from hard to soft state. It seems that the corona evolves from denselow-temperature in the LHS to tenuous high-temperature after the statetransition, which indicates that the state transition is accompanied by theevolution of the coronal properties.

Analysis of the reflection spectra of MAXI J1535-571 in the hard and intermediate states