Physics – Fluid Dynamics
Scientific paper
Jul 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aipc..714..383t&link_type=abstract
X-RAY TIMING 2003: Rossie and Beyond. AIP Conference Proceedings, Volume 714, pp. 383-386 (2004).
Physics
Fluid Dynamics
1
X-Ray, Neutron Stars, Black Holes, Infall, Accretion, And Accretion Disks
Scientific paper
We present a new theoretical framework for interpreting observed spectral/temporal characteristics of accreting neutron star and black hole systems as gravity wave (g-mode oscillations). This model successfully incorporates features of earlier models (published by the present authors and colleagues over the last several years) into a more general scheme that reduces in one limit to a classic treatment by Chandrasekhar, placing this paradigm in the tradition of his analysis. It goes beyond his treatment in the inclusion of radial dependence, the incorporation of MHD, and the application to X-ray timing phenomenology. The conceptual picture that goes with this idea is one in which the problem of disk accretion onto a (symmetrical) black hole is the starting point; accretion in geometries where symmetries are broken by magnetic fields is treated with extensions or perturbations to that case. Primary emphasis is on understanding QPO features and power spectrum breaks. Pairs or groups of QPOs that evolve in correlated ways are treated as splittings of eigenfrequencies in a fluid dynamics analysis rather than, say, as beat phenomena. One particular QPO is identified with the Kepler (gravitational) frequency and the other QPOs are related to that one. Because the Kepler frequency is Newtonian and not a General Relativistic effect, the entire treatment is Newtonian, but this helps explain how certain relationships appear to extend over ~ six orders of magnitude in frequency, linking white dwarfs, neutron stars, and black holes in a single comprehensive picture. The explanatory range of the theoretical framework is considerable: it addresses the magnetic field strength and configuration near the compact object, the 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. Successes of earlier treatments, for example fitting the correlated drifts of as many as six persistent power density spectrum features (QPOs or breaks) with minimal parametrization are retained in the new unified scheme. Presented calculations are aimed at (i) extending the explanatory range of the model, (ii) working out details and consequences of the new framework that unifies it with Chandrasekhar's analysis, (iii) making it explicitly an MHD model and not simply hydrodynamics, and (iv) validating it with test. The goal is to have a theoretical synthesis of the existing QPO phenomenology that will serve as a starting point for future X-ray timing observations.
Titarchuk Lev
Wood Kent S.
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