A possible signature of Lense-Thirring precession in dipping and eclipsing neutron-star low-mass X-ray binaries

Abstract

Relativistic Lense-Thirring precession of a tilted inner accretion disk around a compact object has been proposed as a mechanism for low-frequency (~0.01-70 Hz) quasi-periodic oscillations (QPOs) in the light curves of X-ray binaries. A substantial misalignment angle (~15-20 degrees) between the inner-disk rotation axis and the compact-object spin axis is required for the effects of this precession to produce observable modulations in the X-ray light curve. A consequence of this misalignment is that in high-inclination X-ray binaries the precessing inner disk will quasi-periodically intercept our line of sight to the compact object. In the case of neutron-star systems this should have a significant observational effect, since a large fraction of the accretion energy is released on or near the neutron-star surface. In this Letter I suggest that this specific effect of Lense-Thirring precession may already have been observed as ~1 Hz QPOs in several dipping/eclipsing neutron-star X-ray binaries.