Broad-band spectral-timing analysis on MAXI J1820+070 with Insight-HXMT data

Low-frequency Quasi-Periodic Oscillations (LFQPOs) are commonly observed in black hole binaries while their physical origin is still unclear. However, observations have revealed that LFQPOs are strongly correlated with spectral properties. Studying such correlations could allow us to probe into the physics near the innermost region of the accreting system. In this work, We perform detailed broad-band spectral-timing analyses of the black hole binary MAXI J1820+070 observed by Hard X-ray Modulation Telescope (Insight-HXMT) through its entire 2018 outburst. LFQPOs are detected up to 200 keV during the initial Bright-Hard State (BHS), which suggests the signals directly come from the hot corona; the QPO frequencies are below 0.5 Hz, and do not present any energy dependence, in contrast with observations in a number of other observations. The energy spectra in the 2-150 keV band are analyzed through X-ray reflection spectroscopy. We show that the sources can be classified into different phases in the BHS as traced on the Hardness-Intensity Diagram. We find a strong correlation between the QPO frequency and powerlaw photon index, and the trend differs between phases. We plan to implement more sophisticated reflection model to account for the spectral features and provide a more physical description of the source.