These concepts regarding QPO origins motivate correlation studies that compare QPO frequencies and amplitudes with various spectral parameters. In Figure 10 we show an example of such a correlation between LFQPO frequency and disk flux for two sources. The X-ray states are symbol coded, using the conventions adopted in §5. The QPO frequencies in the hard and intermediate states are highly correlated with disk flux, but this is not true for the QPOs at higher frequency in the SPL state. Presently, there is no explanation for this result. Possibly, the QPO mechanisms could differ between the hard and SPL states, or there could be a common mechanism that exhibits some type of dynamical saturation as the source moves into the SPL state.
Source: Remillard & McClintock 2006 ┃ X-Ray Properties… ⚬𓂃
(echo:: @ ᯤ)