2025ApJ...995L..30S

Dynamic processes in the accretion flow near black holes produce X-ray flux variability, sometimes quasiperiodic. Determining its physical origin is key to mapping the accretion geometry but remains unresolved. We perform a novel phase-resolved analysis on a newly discovered quasiperiodic oscillation (QPO) in the active galactic nucleus 1ES 1927+654. For the first time in a supermassive black hole (SMBH), we detect a unique “U”-shaped QPO lag-energy spectrum and observe coronal spectral variability over the QPO phase. We find that the QPO is adequately explained by plasma resonant oscillations within a corona. The modeling of the QPO spectral properties reveals that the corona is contracting and confined to regions of only a few gravitational radii near the SMBH, consistent with theoretical predictions for a decreasing QPO period of near 10 minutes. These results present the first observational evidence for an oscillating and contracting compact corona around an SMBH.