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Here we present a detailed study of the broadband noise in the power densityspectra of the black hole X-ray binary MAXI J1820+070 during the hard state ofits 2018 outburst, using the Hard X-ray Modulation Telescope (Insight-HXMT)observations. The broadband noise shows two main humps, which might separatelycorrespond to variability from a variable disk and two Comptonization regions.We fitted the two humps with multiple Lorentzian functions and studied theenergy-dependent properties of each component up to 100--150 keV and theirevolution with spectral changes. The lowest frequency component is consideredas the sub-harmonic of QPO component and shows different energy dependencecompared with other broadband noise components. We found that although thefractional rms of all the broadband noise components mainly decrease withenergy, their rms spectra are different in shape. Above $\sim$ 20--30 keV, thecharacteristic frequencies of these components increase sharply with energy,meaning that the high-energy component is more variable on short timescales.Our results suggest that the hot inner flow in MAXI J1820+070 is likely to beinhomogeneous. We propose a geometry with a truncated accretion disk, twoComptonization regions.

The accretion flow geometry of MAXI J1820+070 through broadband noise research with Insight-HXMT