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

TL;DR

This study analyzes the evolution of quasi-periodic oscillations and reflection features in the black hole binary 4U 1630-47 during its 2021 outburst, revealing correlations that support a precessing inner flow model and suggesting different origins for QPOs and QRMs.

Contribution

It provides detailed observational evidence of QPO and QRM evolution and their relation to reflection features, supporting the precessing inner flow model and proposing different origins for QPOs and QRMs.

Findings

QPO frequencies evolve from 1.6 to 3.6 Hz.

Reflection fraction correlates with hardness ratio during QPO detection.

QPO centroid frequency is anti-correlated with reflection fraction.

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.