Lense-Thirring Precession and Quasi-periodic Oscillations in Low-Mass X-Ray Binaries
Abstract
Relativistic dragging of inertial frames around fast-rotating collapsed stars is substantial and can give rise to observable effects. We consider kHz quasi-periodic oscillation (QPO) sources, low-mass X-ray binaries (LMXRBs) containing an accreting neutron star. Within beat frequency models, both the Keplerian frequency of the innermost region of the accretion disk (~0.3-1.2 kHz) and the neutron star spin frequency (~0.3-0.4 kHz) are directly observed. From these, the Lense-Thirring precession frequency (tens of Hz) of the same material as gives rise to the kHz QPOs is determined within a factor of ~4, depending on the neutron star equation of state. The classical contribution from neutron star oblateness decreases the precession frequency slightly. The broad peaks at frequencies ~20-40 Hz in the power spectra of the ``Atoll'' sources 4U 1728-34, 4U 0614+091, and KS 1731-260 and their variations with the higher kHz QPO frequency are well matched by Lense-Thirring precession of material in the innermost disk region. We also suggest that the ~15-50 Hz horizontal branch QPOs of GX 5-1 and GX 17+2 (and likewise other Z-type LMXRBs) arise from the same mechanism.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 1998
- DOI:
- 10.1086/311075
- arXiv:
- arXiv:astro-ph/9709085
- Bibcode:
- 1998ApJ...492L..59S
- Keywords:
-
- ACCRETION;
- ACCRETION DISKS;
- RELATIVITY;
- STARS: PULSARS: GENERAL;
- STARS: NEUTRON;
- STARS: ROTATION;
- X-RAYS: STARS;
- Accretion;
- Accretion Disks;
- Stars: Pulsars: General;
- Relativity;
- Stars: Neutron;
- Stars: Rotation;
- X-Rays: Stars;
- Astrophysics
- E-Print:
- Accepted for publication in Astrophysical Journal Letters. AASTEX needed