Large scaling of BH HF QPO frequencies vs. Keplerian frequencies in the accretion disk. The upper left corner of the plot corresponds to Galactic microquasar BHs, while the lower right corner corresponds to supermassive BHs. The light orange region denotes the ISCO frequencies in the range of a ∈ [0, 1]. The gray area indicates frequencies that are higher than the ISCO frequency. The light yellow area denotes Keplerian frequencies in the inner part of the (thin) disk that radiates more than 90% of the whole disk luminosity (a ≥ 0, see Sect. 3). The green circles denote intermediate-mass BH sources whose mass estimate is based either fully or in a large part on the observations of HF QPOs. For some sources, the error bars are smaller than the displayed symbols.
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