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

TL;DR

This paper proposes that observed ~1 Hz QPOs in dipping and eclipsing neutron-star X-ray binaries may be signatures of Lense-Thirring precession of the inner accretion disk, linking relativistic effects to observable X-ray modulations.

Contribution

It suggests a novel observational signature of Lense-Thirring precession in neutron-star binaries, connecting theoretical predictions with existing QPO observations.

Findings

~1 Hz QPOs may be caused by precessing inner accretion disks.

High-inclination systems show effects consistent with Lense-Thirring precession.

Potential observational evidence for relativistic frame-dragging effects.

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.