Power spectral densities of the X-ray variability of the compact stellar cluster with an IMBH. Left: PSD of the X-ray light curve produced by the near-horizon flow around the IMBH as calculated from an ADAF model, which has a flat power-law slope of ∼ − 0.53. Right: PSD of the total X-ray light curve, which exhibits a steeper power-law slope of ∼ − 1.41. The points represent mean PSD values within the ten regular logarithmic bins in frequency, while the error bars represent standard deviations in these bins. We fit the power-law functions to these binned PSD values for consistency. In both panels, the extents of the logarithms of PSDs and frequencies are kept the same for consistency and easier comparison.