English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Although low-frequency quasiperiodic oscillations (LFQPOs) are commonlydetected in the X-ray light curves of accreting black hole X-ray binaries,their origin still remains elusive. In this study, we conduct phase-resolvedspectroscopy in a broad energy band for LFQPOs in MAXI J1820+070 during its2018 outburst, utilizing Insight-HXMT observations. By employing theHilbert-Huang transform method, we extract the intrinsic quasiperiodicoscillation (QPO) variability, and obtain the corresponding instantaneousamplitude, phase, and frequency functions for each data point. Withwell-defined phases, we construct QPO waveforms and phase-resolved spectra. Bycomparing the phase-folded waveform with that obtained from the Fourier method,we find that phase folding on the phase of the QPO fundamental frequency leadsto a slight reduction in the contribution of the harmonic component. Thissuggests that the phase difference between QPO harmonics exhibits timevariability. Phase-resolved spectral analysis reveals strong concurrentmodulations of the spectral index and flux across the bright hard state. Themodulation of the spectral index could potentially be explained by both thecorona and jet precession models, with the latter requiring efficientacceleration within the jet. Furthermore, significant modulations in thereflection fraction are detected exclusively during the later stages of thebright hard state. These findings provide support for the geometric origin ofLFQPOs and offer valuable insights into the evolution of the accretion geometryduring the outburst in MAXI J1820+070.

A Phase-resolved View of the Low-frequency Quasiperiodic Oscillations from the Black Hole Binary MAXI J1820+070