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L. Titarchuk (Naval Research Laboratory and George Mason University/CEOSR), K. Wood (Naval Research Laboratory)
We present a comprehensive, physical, framework for interpreting spectral/temporal characteristics (QPOs, PDS breaks) of accreting black hole, neutron star, and white dwarf systems as gravity wave (g-mode oscillations). It incorporates features of earlier models by the authors and collaborators in a more general scheme that reduces in one limit to a classic treatment by Chandrasekhar. It goes beyond his treatment by inclusion of radial dependence, incorporation of MHD, and application to X-ray timing phenomenology. The physical picture starts with disk accretion onto a (symmetrical) black hole; accretion in geometries where symmetries are broken by magnetic fields is treated as an extension of that case. Pairs or groups of QPOs with correlated frequency drifts are treated as splittings of eigenfrequencies in a fluid dynamics analysis, rather than as beat phenomena. One particular QPO is identified with the gravitational (essentially Kepler) frequency and other QPOs are related to that one. Having the basic frequency be the gravitational frequency, which is Newtonian and not a General Relativistic effect, helps explain how certain relationships can extend over ~five orders of magnitude in frequency, linking white dwarfs, neutron stars, and black holes. The explanatory range of the model is considerable: it addresses the magnetic field strength and configuration near the compact object, extension of the Keplerian disk near the central object (and the location of the transition between Keplerian and non Keplerian flow), the presence of advection flow along with disk accretion and the conditions for shock formation in the accretion flow. Many of these topics have been addressed in the earlier papers are the background to this model. Successes of earlier treatments, for example fitting the correlated drifts of as many as six persistent PDS features (QPOs or breaks) with minimal parametrization are preserved.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.