SIMBAD references

The Galactic black hole X-ray binary 4U 1630-47 went into a new outburst in 2021 after ∼600 days from its 2020 outburst. We perform a detailed analysis of quasiperiodic oscillations and spectral evolutions during its 2021 outburst based on Insight-HXMT observations. The main science aims to study the reflection features and evolution of this accreting black hole using the observations of detecting quasiperiodic oscillations (QPOs) and quasi-regular modulations (QRMs). The QPOs frequencies evolve from ∼1.6 to 3.6 Hz, and QRMs have low frequencies around 0.05-0.07 Hz. The reflection fraction varies during the outburst and has a positive correlation with the hardness ratio when QPOs are detected. The centroid frequency of QPOs is anticorrelated to the reflection fraction. This is consistent with the prediction of the precessing inner flow model and provides evidence for a geometrical origin of QPOs. The centroid frequency of QRMs also shows an anticorrelation to the reflection fraction, but the hardness ratio shows no relation to the reflection fraction during the period. We suggest that QRMs may have a different origin from QPOs and be caused by instabilities in the corona.