Temporal and Spectral Evolution of MAXI J1348 –630 During 2019 Outburst

ABSTRACT

Stellar‐mass black hole x‐ray binaries serve as key testbeds for accretion and strong gravity theories, while full‐cycle spectral observations are still limited to verify the disk‐truncation framework. We conduct continuous time‐resolved spectroscopy covering the entire 2019 outburst of MAXI J1348–630 (from MJD 58510.25 to 58693.49, spanning approximately 183.2 days) with Insight‐HXMT data. The source displays textbook counterclockwise Q‐shaped hysteresis on the hardness‐intensity diagram, and the luminosity gap between forward and reverse transitions arises from mismatched viscous response times of the disk and corona. The apparent inner disk radius drops to unphysical values (e.g., ) in the hard state due to strong Comptonization, rises to a soft‐state mean of , and peaks at in the very soft state. This soft‐state plateau, peaking close to the theoretical ISCO radius of for , solidly proves that thin accretion disks reach the innermost stable circular orbit, further backed by the soft‐state anticorrelation between disk temperature and normalization. The photon index rises from a hard‐state mean of to a soft‐state mean of following standard Compton cooling behavior, while the powerlaw normalization peaks in truncated hard states. Disk‐corona coupling only strengthens during rapid state shifts, with a weak corona decoupled from the dominant thermal disk at high accretion rates. This full multi‐parameter observational sequence provides definitive support for unified accretion transition theory and yields new quantitative constraints on disk‐corona interplay among transient black hole binaries.