Lense-Thirring precession and quasi-periodic oscillations in X-ray binaries

D. Markovic et Fk. Lamb, Lense-Thirring precession and quasi-periodic oscillations in X-ray binaries, ASTROPHYS J, 507(1), 1998, pp. 316-326
Citations number
Categorie Soggetti
Space Sciences
Journal title
ISSN journal
0004-637X → ACNP
Year of publication
316 - 326
SICI code
It has recently been suggested that gravitomagnetic precession of the inner part of the accretion disk, possibly driven by radiation torques, may be r esponsible for some of the quasi-periodic X-ray brightness oscillations (QP Os) and other spectral features with frequencies between 20 and 300 Hz obse rved in the power spectra of some low-mass binary systems containing accret ing neutron stars and black hole candidates. We have explored the free and driven normal modes of geometrically thin disks in the presence of gravitom agnetic and radiation warping torques. We have found a family of low-freque ncy gravitomagnetic (LFGM) modes with precession frequencies that range fro m the lowest frequency allowed by the size of the disk up to a certain crit ical frequency omega(crit), which is similar to 1 Hz for a compact object o f solar mass. The lowest frequency (lowest order) LFGM modes are similar to the previously known radiation warping modes, extend over much of the disk , and have damping rates greater than or similar to 10 times their precessi on frequencies. The highest frequency LFGM modes are tightly wound spiral c orrugations of the disk that extend to similar to 10 times its inner radius and have damping rates greater than or similar to 10(3) times their preces sion frequencies. A radiation warping torque can cause a few of the lowest frequency LFGM modes to grow with time, but even a strong radiation warping torque has essentially no effect on the LFGM modes with frequencies greate r than or similar to 10(-4) Hz. We have also discovered a second family of high-frequency gravitomagnetic (HFGM) modes with precession frequencies tha t range from omega(crit) up to slightly less than the gravitomagnetic prece ssion frequency omega(gm,i) of a particle at the inner edge of the disk, wh ich is 30 Hz if the disk extends inward to the innermost stable circular or bit around a 2 M. compact object with dimensionless angular momentum cJ/GM( 2) = 0.2. The lowest frequency HFGM modes are very strongly damped and have warp functions and precession frequencies very similar to those of the hig hest frequency LFGM modes. In contrast, the highest frequency (lowest order ) HFGM modes are very localized spiral corrugations of the inner disk and a re weakly damped, with Q-values of similar to 2-50. We discuss the implicat ions of our results for the observability of Lense-Thirring precession in X -ray binaries.