The Spin Measurement of the Black Hole SLX 1746-331 Using Insight-HXMT Observations

Abstract We present an X-ray spectral analysis of a black hole X-ray binary, SLX 1746-331, during the 2023 outburst using five Insight-HXMT observations. We jointly use the reflection model relxillcp and the general relativistic thermal thin disk model kerrbb to fit the spectra from 2 to 100 keV. By jointly fitting the five spectra, we constrain the black hole mass to be M = 5.8 ± 0.3 M ⊙ and the dimensionless spin parameter to be <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>a</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.8</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.02</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.01</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> (90% statistical confidence). The reflection model shows that SLX 1746-331 is a high-inclination system with the inclination angle <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>i</mml:mi> <mml:mo>=</mml:mo> <mml:mn>63</mml:mn> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">°</mml:mi> </mml:mrow> </mml:mover> <mml:msubsup> <mml:mn>7</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.3</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , and the accretion disk has a density <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">log</mml:mi> <mml:mi>N</mml:mi> <mml:mo>∼</mml:mo> <mml:mn>16</mml:mn> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:math> . In addition, with the different reflection model relxilllp , which assumes a lamppost geometry corona, we still obtain similar results.