Fundamental frequencies of strong field geodetic motion and QPOs in low-mass X-ray binaries

The relativistic precession model for quasi-periodic oscillations (QPOs) in low-mass X-ray binaries is reviewed. The behaviour of three simultaneous types of QPOs is well matched in terms of the fundamental frequencies for geodesic motion in the strong field of the accreting compact object for reasonable star masses and spin frequencies. The model works for neutron star as well as black hole candidate systems, as it ascribes the higher frequency kHz QPOs, the lower frequency kHz QPOs and the horizontal branch oscillations to the Keplerian, periastron precession and nodal precession frequencies of matter orbiting close to the inner edge of the accretion disk. The remarkable correlation between the centroid frequency of QPOs in both neutron star and black hole candidate low-mass X-ray binaries is very well fit by the model. Some testable predictions of the model are described. QPOs from low-mass X-ray binaries might provide an unprecedented laboratory to test general relativity in the strong field regime