Fig. 2
Left: behaviour of the epicyclic frequencies for a = 1.04. The three possible QPO excitation radii determined within the Ep model are denoted by the dotted vertical lines. We note that more than one extremum of the epicyclic frequencies related to accretion discs appear only when a ∈ (0.952, 1.089). Right: frequency ratio RRP1 determined within the RP1 model for various values of a. We note that the observed 3:2 ratio is not allowed by the model when a> 1.4.
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