Estimating the Black Hole Spin for the X-Ray Binary MAXI J1727-203 Based on Insight-HXMT

Abstract

We constrain the spin of the black hole candidate MAXI J1727-203 using Insight-HXMT data. Due to limited Insight-HXMT observations covering only part of the outburst, NICER data were used to analyze the full outburst’s state transitions; we identified two of three HXMT observations in the high soft state and applied the continuum-fitting method to measure the spin. Based on previous estimates and continuum spectral fittings, we explored the parameter space and found that the best-fitting values were (D, i, M) ≈ (6 kpc, 30°, 12 M⊙). We also tested the variation of these parameters using Monte Carlo simulations, sampling over 3000 sets within the parameter ranges 5.9 kpc < D < 7 kpc, 24° < i < 35°, and 10 M⊙ < M < 14 M⊙, yielding a spin measurement of (1σ). In addition, we analyzed NuSTAR data in the low hard state and found a good fit with the tbabs∗(diskbb+powerlaw) model, with no significant iron line features observed in the residuals; therefore, the previous reflection model results suggesting an extremely high spin overestimates the black hole spin.