The black hole candidate system SLX 1746--331 was back to business in 2023, after a long silence of roughly 13 years. An outburst was observed thoroughly by \textit{ Insight}-HXMT and \textit{ NICER}. The outburst is characterized by spectral dominance of the soft state, where the joint \textit{ Insight}-HXMT and \textit{ NICER} spectral analysis shows the temperature dependence of the disk flux follows $T_{ \rm in}^{ 3.98}$, and thus suggests that the inner disk reaches to ISCO during almost the entire outburst. By assuming 0.3 $L_{ \rm Edd}$ for the peak flux and an inclination angle of zero degrees, the lower limit of the compact object hosted in this system is estimated as 3.28$\pm 2.14 M_\odot$. We also look into the relation of the disk temperature and disk flux for a sample of black hole systems, and by taking the disk temperature derived in the outburst of SLX 1746--331, such a relation results in a mass estimation of $5.2 \pm 4.5M_\odot$. Finally, the spin of the compact object is constrained to larger than 0.8 with a spectral model of kerrbb.
Categories: astro-ph.HE astro-ph.SR