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We provided a comprehensive study of the properties of the black hole in the low-mass X-ray binary system 4U 1543-47, specifically focusing on the 2021 outburst (MJD 59380–59470). Using observations from the Insight - HXMT mission, we employed X-ray reflection fitting method and analysed spectral data to estimate key black hole parameters. Through our investigation redbased on 6 out of the 52 available observations, we estimated the spin parameter of the black hole to be |$0.902_{-0.053}^{+0.054}$| and the inclination angle of the accretion disc to be |$28.91_{-1.24}^{+1.82}$| ° (90 per cent confidence limits, statistical only), then we discussed the influence of high luminosity. Based on the relxill series models are not suitable for thick disc scenario, and in comparison with findings from other studies, we propose that our estimation of the spin value may be exaggerated. [ABSTRACT FROM AUTHOR]

We report the results of fitting Insight-HXMT data to the black hole X-ray binary MAXI J1348-430, which was discovered on January 26th, 2019, We also inferred the ionization state and iron abundancewith the Gas Slit Camera on-board MAXI. Several observations at the beginning of the first burst were selected, with a total of 10 spectra. From the residuals of fits using disc plus power-law models, X-ray reflection signatures were clearly visible in some of these observations. We use the state-of-the-art |$\tt {relxill}$| series reflection model to fit six spectra with distinct reflection signatures and a joint fit to these spectra. In particular, we focus on the results for the black hole spin values. Assuming R in = R ISCO, the spin parameter is constrained to be |$0.82^{+0.04}_{-0.03}$| with 90 per cent confidence level (statistical only). [ABSTRACT FROM AUTHOR]

MAXI J1803−298, a newly-discovered Galactic transient, and black hole candidate was first detected by MAXI /GSC on 2021 May 01. 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 NuSTAR and NICER /XTI on the same day over the energy range between 0.7–79.0 keV in SIMS state, and the observed inner radius of the accretion disc is demonstrated to have extended to the ISCO radius (R in =1.08 R ISCO). Implementing the relativistic reflection model relxillCp , we found its spin (and the inclination angle i) can be constrained to be close to an extreme value, 0.991 (i ∼ 70 °), at 68 per cent confidence interval. The results suggest that MAXI J1803−298 may be a fast-rotating black hole with a large inclination angle. [ABSTRACT FROM AUTHOR]

The black hole candidate MAXI J1348-630 was discovered in 2019 January 26, with the Gas Slit Camera (GSC) on-board MAXI. We report a detailed spectral analysis of this source by using the archived data of NuSTAR. A total of nine observations covered the complete outburst evolution of MAXI J1348-630 from the hard state to the soft state and finally back to the hard state. Additionally, the intermediate state is found in the transition from the hard state to the soft state. We use the state-of-the-art reflection model relxill family to fit all the nine spectra, and the spectra from two focal plane module detectors of NuSTAR are jointly fitted for each observation. In particular, we concentrate on the results of the black hole spin parameter and the inclination of the accretion disc. Based on the analysis of the inner radius of the accretion disc, we obtain the spin parameter |$a_* =0.78_{-0.04}^{+0.04}$|⁠ , and the inclination angle of the inner disc |$i = 29.2_{-0.5}^{+0.3}$| °. Furthermore, we also find that when the black hole is in the hard state, the accretion disc would show a significant truncation. The high iron abundance and ionization of the accretion disc obtained in the fitting results can be possibly explained by the high density of the accretion disc. [ABSTRACT FROM AUTHOR]

MAXI J1820+070 is a newly discovered black hole X-ray binary, whose dynamical parameters, namely the black hole mass, the inclination angle, and the source distance, have recently been estimated. Insight-HXMT have observed its entire outburst from 2018 March 14. In this work, we attempted to estimate the spin parameter a*, using the continuum-fitting method and applying a fully relativistic thin disk model to the soft-state spectra obtained by Insight-HXMT. It is well known that a* is strongly dependent on three dynamical parameters in this method, and we have examined two sets of parameters. Adopting our preferred parameters: M = , i = 63° ± 3°, and D = 2.96 ± 0.33 kpc, we found a slowly spinning black hole of a* = 0.14 ± 0.09 (1σ), which gives a prograde spin parameter as the majority of other systems show. It is also possible for the black hole to have a retrograde spin (less than 0) if different dynamical parameters are taken. [ABSTRACT FROM AUTHOR]