Quasi-periodic oscillations and reflection feature evolution in 4U 1630-47 observed with Insight-HXMT

Abstract: The Galactic black hole (BH) X-ray binary 4U 1630-47 went into a new outburst in 2021 after $\sim$ 600 days from its 2020 outburst. We perform a detailed analysis of quasi-periodic oscillations and spectral evolutions during its 2021 outburst based on \textit{Insight}-HXMT observations. The main science aims to study the reflection features evolution of this accreting black hole using the observations of detecting quasi-periodic oscillations (QPOs) and quasi-regular modulations (QRMs). The QPOs frequencies evolve from $\sim 1.6 - 3.6$ 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 anti-correlated to the reflection fraction. This is consistent with the prediction of precessing inner flow model and provides evidence for a geometrical origin of QPOs. The centroid frequency of QRMs also shows an anti-correlation 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.