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 correlat ion extends over nearly three decades in frequency and encompasses both neu tron star and black hole candidate systems Bi We discuss this result In lig ht of the relativistic precession model, which has been proposed to interpr et the kilohertz quasi-perodic oscillations (QPOs) as well as some of the l ower frequency QPOs of neutron star low-mass X-ray binaries of the atoll an d Z classes. Unlike other models, the relativistic precession model does no t require the compact object to be a neutron star and can be applied to bla ck hole candidates as well. We show that the predictions of the relativisti c precession model match both the value and dependence of the correlation t o very good accuracy and without resorting to additional assumptions.