Global oscillations of a fluid torus as a modulation mechanism for black-hole high-frequency QPOs

We study strong‐gravity effects on modulation of radiation emerging from accreting compact objects as a possible mechanism for flux modulation in QPOs. We construct a toy model of an oscillating torus in the slender approximation assuming thermal bremsstrahlung for the intrinsic emissivity of the me...

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Bibliographic Details
Published in:Astronomische Nachrichten 2005-11, Vol.326 (9), p.849-855
Main Author: Bursa, M.
Format: Article
Language:English
Subjects:
gravitation
quasi-periodic oscillations
X-rays: variability
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Summary:We study strong‐gravity effects on modulation of radiation emerging from accreting compact objects as a possible mechanism for flux modulation in QPOs. We construct a toy model of an oscillating torus in the slender approximation assuming thermal bremsstrahlung for the intrinsic emissivity of the medium and we compute observed (predicted) radiation signal including contribution of indirect (higher‐order) images and caustics in the Schwarzschild spacetime. We show that the simplest oscillation mode in an accretion flow, axisymmetric up‐and‐down motion at the meridional epicyclic frequency, may be directly observable when it occurs in the inner parts of accretion flow around black holes. Together with the second oscillation mode, an in‐and‐out motion at the radial epicyclic frequency, it may then be responsible for the high‐frequency modulations of the X‐ray flux observed at two distinct frequencies (twin HF‐QPOs) in micro‐quasars. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
ISSN:0004-6337
1521-3994
DOI:10.1002/asna.200510426