The Hot Accretion Flow Evolution in the Black Hole X-Ray Binary MAXI J1348-630

Abstract MAXI J1348-630, as a low-mass black hole binary system in the Galaxy, showed an X-ray outburst in 2019. We analyzed the Insight Hard X-ray Modulation Telescope spectral data in the low hard state and intermediate state during the outburst from MJD 58510 to 58519 at the energy band from 2 to 100 keV. During the entire process, a thin disk extending to the innermost stable circular orbit (ISCO) from a large truncated disk (truncated radius >5 ISCO) suggested the corona geometry evolution. There exist time lags between the radio and hard X-ray flux peaks: the 30–100 keV flux is about 5 days ahead of the radio flux, the 11–30 keV flux is about 4 days ahead, and the reflection fraction is about 2 days ahead, with the accretion disk approaching the ISCO about 1 day before radio peak. This disk–corona–jet coupling and evolution suggest the corona contains two phases of cold dense material and hot gas, with the high-temperature region of the corona cooling fast. The strong radio emission accompanying a thin accretion disk with a relatively high accretion rate favors a magnetic tower jet mechanism.