Insight-HXMT, NICER and NuSTAR views to the newly discovered black hole X-ray binary Swift J151857.0--572147

Abstract

The systematic properties are largely unknown for the black hole X-ray binary Swift J151857.0--572147 newly discovered in the 2024 outburst. The nature of a black hole can be completely defined by specifying the mass and dimensionless spin parameter. Therefore, accurate measurement of the two fundamental parameters is important for understanding the nature of black holes. The joint spectral fitting of a reflection component with simultaneous observations from Insight-HXMT, NICER and NuSTAR reveals for the first time a black hole dimensionless spin of $0.84^{+0.17}_{-0.26}$ and an inclination angle of $21.1^{+4.5}_{-3.6}$ degree for this system. Monitoring of the soft state by NICER results in disk flux and temperature following $F_{\rm disk} \propto T_{\rm in}^{3.83\pm 0.17}$. For the standard thin disk, $L_{\rm disk}\approx 4\pi R_{\rm in}^{2}\sigma T_{\rm in}^{4}$, so the relationship between the flux and temperature of the disk we measured indicates that the inner radius of the disk is stable and the disk is in the Innermost Stable Circular Orbit. With an empirical relation built previously between the black hole outburst profile and the intrinsic power output, the source distance is estimated as $5.8\pm 2.5$ kpc according to the outburst profile and peak flux observed by Insight-HXMT and NICER. Finally, a black hole mass of $3.67\pm1.79-8.07\pm 4.20 M_\odot$ can be inferred from a joint diagnostic of the aforementioned parameters measured for this system. This system is also consistent with most black hole X-ray binaries with high spin and a mass in the range of 5--20 $M_\odot$