The spin of a stellar black hole 4U 1543-47 determined by Insight-HXMT

Abstract

We present a spectral analysis of \textit{Insight}-HXMT observations of the low-mass X-ray binary 4U 1543-47 which locates in our Milky Way galaxy during the 2021 outburst. We focus on the observations in its soft state, and attempt to determine the spin of the black hole candidate through Thermal-Continuum Fitting (CF) method. The spin derived from CF method is highly dependent on black hole mass, distance and inclination angle of inner disk. In this article, we have adopted the preferred range of parameters: $M=9.4\pm 1 M_{\odot}$, D=$7.5{\pm}0.5$ kpc and $i=36.3^{+5.3}_{-3.4}$ degrees. We attain a moderate spin, $a=0.46\pm0.12$, which is consistent with previous results measured in the 2002 outburst. Besides, we notice the spectra show a wide blue shifted absorption feature between 8-10 keV which would originate from the highly ionized iron line. We try to fit the feature with {\em xstar} model and suggest that this feature may come from relativistic disk wind with a velocity of $v_{\rm wind}\sim 0.2c$. We attribute this relativistic disk wind to the super-Eddington accretion during the black hole outburst.