Investigation of Quasiperiodic Oscillations in the Flaring State of Swift J1727.8‐1613 With Insight‐ HXMT During Its 2023 Outburst

ABSTRACT We present a timing analysis of the black hole x‐ray binary Swift J1727.8‐1613 during its 2023 outburst using Insight‐HXMT observations. In the flaring state, we reveal a highly synchronized positive correlation between the quasiperiodic oscillation (QPO) frequency and the x‐ray count rate. Notably, near the count rate peak (around MJD 60206), we detect a dramatic QPO frequency jump from 3.75 to 8.61 Hz, accompanied by a sharp drop in the root mean square (RMS) amplitude to 2.5%. We demonstrate that the fundamental and harmonic frequencies strictly obey a 1:2 ratio, with a fitted slope of 2.0178 ± 0.0066. These results strongly support the Lense–Thirring precession model, indicating that an increased accretion rate shrinks the inner disk radius and decreases the corona's geometric thickness. This work provides crucial observational constraints on the geometric evolution of black hole accretion flows.