Bardeen-Petterson effect and quasi-periodic oscillations in X-ray binaries

The Bardeen-Petterson effect around a rapidly rotating compact object cause s a tilted accretion disk to warp into the equatorial plane of the rotating body. Viscous forces cause the accretion flow to divide into two distinct regions-an inner aligned accretion disk and an outer tilted accretion disk. The transition between these two occurs at a characteristic radius that de pends on the mass and angular momentum of the central object and possibly o n the accretion rate through the disk. We propose that accreting material p assing through the transition region may generate quasi-periodic brightness oscillations such as have been observed in a number of X-ray binaries. We show that this effect may be present in the black hole X-ray binary GRO J16 55-40. We also argue that the quasi-periodic oscillation (QPO) frequency ra nge predicted by this model is consistent with observed QPO frequencies in both black hole and neutron star low-mass X-ray binaries.