Journal Article

On an excitation mechanism for trapped inertial waves in discs around black holes

Bárbara T. Ferreira and Gordon I. Ogilvie

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 386, issue 4, pages 2297-2310
Published in print June 2008 | ISSN: 0035-8711
Published online April 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13207.x
On an excitation mechanism for trapped inertial waves in discs around black holes

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According to one model, high-frequency quasi-periodic oscillations (QPOs) can be identified with inertial waves, trapped in the inner regions of accretion discs around black holes due to relativistic effects. In order to be detected, their amplitudes need to reach large enough values via some excitation mechanism. We work out in detail a non-linear coupling mechanism suggested by Kato, in which a global warping or eccentricity of the disc has a fundamental role. These large-scale deformations combine with trapped modes to generate ‘intermediate’ waves of negative energy that are damped as they approach either their corotation resonance or the inner edge of the disc, resulting in amplification of the trapped waves. We determine the growth rates of the inertial modes, as well as their dependence on the spin of the black hole and the properties of the disc. Our results indicate that this coupling mechanism can provide an efficient excitation of trapped inertial waves, provided the global deformations reach the inner part of the disc with non-negligible amplitude.

Keywords: accretion, accretion discs; black hole physics; hydrodynamics; waves; X-rays: binaries

Journal Article.  9518 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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