On the Optical Emission in the Minioutburst of the Black Hole X-Ray Binary MAXI J1348-630

Abstract We investigate the optical emission of the black hole X-ray binary MAXI J1348-630 during its 2019 minioutburst. Using optical data from the Las Cumbres Observatory Global Telescope and X-ray data from Insight-HXMT, we performed time delay analysis, optical-X-ray correlation analysis, and spectral energy distribution (SED) fitting. Our key findings are as follows: (1) The X-ray Comptonization flux lags behind the optical emission by ∼8.5 days, a delay naturally explained by the disk instability model (DIM). (2) The optical and X-ray fluxes show a power-law correlation with a slope ∼0.4, which lies between the predicted values for viscous heating and X-ray reprocessing, consistent with the DIM framework. (3) SED fitting with the irradiated disk model successfully reproduces the quasi-simultaneous optical and X-ray data, and the contribution of the jet is negligible. Our results indicate that the optical emission during the minioutburst originates from the disk, rather than the jet or hot accretion flow, and highlight the critical role of the DIM in understanding the minioutburst of X-ray binaries.