Kavli Affiliate: Luis C. Ho
| First 5 Authors: Jie Liao, Ning Chang, Lang Cui, Pengfei Jiang, Didong Mou
| Summary:
Type-C quasi-periodic 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 August and September 2023,
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 proposed a scenario to
describe the co-evolution 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 INTEGRAL/IBIS. A phenomenological analysis of the
corona scenario was also conducted.
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