Tracking the Jet-like Corona of Black Hole Swift J1727.8−1613 during a Flare State through Type-C Quasiperiodic Oscillations

Abstract Type-C quasiperiodic oscillations (QPOs) in black hole X-ray transients typically manifest in the low-hard and hard-intermediate states. This study presents a detailed spectral and temporal analysis of the black hole candidate Swift J1727.8−1613 using NICER observations from 2023 August and September, with a focus on the first flare period. We detected Type-C QPOs whose centroid frequency increased from 0.33 Hz to 2.63 Hz. An additional increase in frequency was observed when the outburst entered a flare period. The time-averaged spectra, along with the rms and phase-lag spectra of the QPOs, were jointly fitted using the time-dependent Comptonization model vkompthdk to examine the geometry of the corona during this flare. Correlations between spectral and temporal properties suggest that the detected type-C QPOs are primarily modulated by Lense–Thirring precession. Leveraging simultaneous radio observations that indicate discrete jet ejections, we propose a scenario to describe the coevolution of the disk–corona–jet during a flare (∼3 days). This scenario is partially supported for the first time by polarization data in the soft gamma-ray band from the IBIS instrument on board the International Gamma-Ray Astrophysics Laboratory. A phenomenological analysis of the corona scenario was also conducted.