Journal Article

Twin-peak quasi-periodic oscillations and the kinematics of orbital motion in a curved space–time

Claudio Germanà

in Monthly Notices of the Royal Astronomical Society: Letters

Published on behalf of The Royal Astronomical Society

Volume 430, issue 1, pages L1-L5
Published in print March 2013 |
Published online December 2012 | e-ISSN: 1745-3933 | DOI: https://dx.doi.org/10.1093/mnrasl/sls036

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Twin-peak high-frequency quasi-periodic oscillations (HF QPOs) observed in the power spectra of low-mass X-ray binaries, with either a black hole or a neutron star, have central frequencies that are typical of the orbital motion time-scale close to the compact object. Thus, twin HF QPOs might carry the fingerprint of physical effects in a strongly curved space–time. We study the azimuth phase ϕ(t) for orbital motion in the Schwarzschild metric and calculate the power spectra to check whether they display the features seen in the observed ones. We show that the timing of ϕ(t) on non-closed orbits can account for the observed twin-peak HF QPOs. The uppermost couple of peaks in frequency has the lower peak that corresponds to the azimuthal frequency νϕ, the upper one to νϕr.

The azimuth phase temporal behaviour ϕ(t) on a slightly eccentric orbit in the Schwarzschild metric is described by a linear function of slope νϕ plus an oscillating term at the relativistic radial frequency νr. We deduce that the twin-peak HF QPOs might originate from a frequency modulated signal driven by the kinematics of orbital motion in a curved space–time.

Keywords: accretion, accretion discs; black hole physics; gravitation; methods: numerical; X-rays: binaries

Journal Article.  3237 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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