Left: BH mass versus photon index for the SMBH accreting systems in which QPOs are detected, with ultrasoft AGNs highlighted in red. The red star represents J1302. The photon index was derived from the spectral fitting with a simple absorbed power-law model to the soft X-ray spectrum below 2 keV. For a comparison, we overplot the AGN sample of González-Martín & Vaughan (2012) in which QPOs were searched uniformly (light blue), but not found (except for RE J1034+36). Errors on the photon index are given by spectral fittings, corresponding to 90% confidence level for one parameter of interest (Δχ² = 2.706). The BH masses from the AGN sample of González-Martín & Vaughan (2012) have characteristic errors of ∼0.5 dex (Vestergaard & Peterson 2006). Right: same as left, but for the plot of Eddington ratio versus photon index. Errors on the Eddington ratios are not shown due to the large uncertainties inherent in determining bolometric luminosity and BH mass. Distributions of the BH mass and Eddington ratio and are shown on the top panel, while the distribution of the photon index is shown on the right panel.