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Oscillations of tori in the pseudo-Newtonian potential

Journal article
Authors Eva Srámková
Ulf Torkelsson
Marek A Abramowicz
Published in Astronomy and astrophysics
Volume 467
Issue 2
Pages 641-646
ISSN 00046361
Publication year 2007
Published at Department of Physics (GU)
Pages 641-646
Language en
Keywords accretion: accretion disks, black hole physics
Subject categories High energy astrophysics, Theory of relativity, gravitation


Context: The high-frequency quasi-periodic oscillations (HF QPOs) in neutron star and stellar-mass black hole X-ray binaries may be the result of a resonance between the radial and vertical epicyclic oscillations in strong gravity. Aims: In this paper we investigate the resonant coupling between the epicyclic modes in a torus in a strong gravitational field. Methods: We perform numerical simulations of axisymmetric constant angular momentum tori in the pseudo-Newtonian potential. The epicyclic motion is excited by adding a constant radial velocity to the torus. Results: We verify that slender tori perform epicyclic motions at the frequencies of free particles, but the epicyclic frequencies decrease as the tori grow thicker. More importantly, and in contrast to previous numerical studies, we do not find a coupling between the radial and vertical epicyclic motions. The appearance of other modes than the radial epicyclic motion in our simulations is rather due to small numerical deviations from exact equilibrium in the initial state of our torus. Conclusions: We find that there is no pressure coupling between the two axisymmetric epicyclic modes as long as the torus is symmetric with respect to the equatorial plane. However we also find that there are other modes in the disc that may be more attractive for explaining the HF QPOs.

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