Correlations in the Quasi-periodic Oscillation Frequencies of Low-Mass X-Ray Binaries and the Relativistic Precession Model

A remarkable correlation between the centroid frequencies of quasi-periodic oscillations (or peaked noise components) from low-mass X-ray binaries has been recently discovered by Psaltis, Belloni, & van der Klis. This correlation extends over nearly three decades in frequency and encompasses both neutron star and black hole candidate systems. We discuss this result in light of the relativistic precession model, which has been proposed to interpret the kilohertz quasi-periodic oscillations (QPOs) as well as some of the lower frequency QPOs of neutron star low-mass X-ray binaries of the atoll and Z classes. Unlike other models, the relativistic precession model does not require the compact object to be a neutron star and can be applied to black hole candidates as well. We show that the predictions of the relativistic precession model match both the value and dependence of the correlation to very good accuracy and without resorting to additional assumptions.