Back to business: SLX 1746--331 after 13 years of silence

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 $\mathit{\text{Insight}}$-HXMT and $\mathit{\text{NICER}}$. The outburst is characterized by spectral dominance of the soft state, where the joint $\mathit{\text{Insight}}$-HXMT and $\mathit{\text{NICER}}$ spectral analysis shows the temperature dependence of the disk flux follows $T_{\mathrm{i}\mathrm{n}}^{3.98}$, and thus suggests that the inner disk reaches to ISCO during almost the entire outburst. By assuming 0.3 $L_{\mathrm{E}\mathrm{d}\mathrm{d}}$ 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$\pm 2.14M_{\odot }$. 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.