The spins of the Galactic black holes in MAXI J1535-571 and 4U 1630-472 from Insight-HXMT

Abstract

Insight-HXMT is the first Chinese X-ray astronomical mission. With a 1-250 keV bandpass, an energy resolution of 150 eV at 6 keV, and without being subject to pile-up distortions, it is suitable to study bright X-ray sources like Galactic black holes. In the present paper, we study Insight-HXMT observations of the X-ray binaries MAXI J1535-571 and 4U 1630-472 during their outbursts in 2017 and 2020, respectively. From the analysis of the reflection features, we are able to infer the black hole spin parameter in the two sources. For MAXI J1535-571, we find a spin parameter very close to 1, a * = 0.9916 ± 0.0012 (90% C.L.), which is consistent with the previous NuSTAR measurement. For 4U 1630-472, we find a moderately high value of the black hole spin parameter, a * = 0.817 ± 0.014 (90% C.L.), which is lower than the almost extremal value found with NuSTAR data.

An Insight-HXMT view of the mHz quasi-regular modulation phenomenon in the black hole X-ray binary 4U 1630-47

“…A potential distance of 4.7−11.5 kpc was obtained by investigating the dust-scattering halo created by 4U 1630-47 (Kalemci et al 2018). Liu et al (2021) suggested a moderately high spin of 𝑎 * = 0.817 ± 0.014 (90% confident level) by fitting the reflection spectra of Insight-HXMT during its 2020 outburst. This value is lower than what had been reported by King et al (2014), in which they suggested an extreme high spin of 𝑎 * = 0.985 +0.005 −0.014 and an inclination angle of 𝑖 = 64 +2 −3 deg by fitting the NuSTAR spectra.…”