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

Abstract

Twin peak high frequency quasi-periodic oscillations (HF QPOs) observed in the power spectra of Low Mass X-ray Binaries (LMXBs), 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 ν_ϕ, the upper one to ν_ϕ+ν_r. The azimuth phase temporal behavior ϕ(t) on a slightly eccentric orbit in the Schwarzschild metric is described by a linear function of slope ν_ϕ plus an oscillating term at the relativistic radial frequency ν_r. We deduce that the twin peak HF QPOs might originate from a frequency modulated (FM) signal driven by the kinematics of orbital motion in a curved space-time.

5 pages, 3 figures. Accepted for publication in MNRAS Letters

References in corpus (6)

• X-ray Properties of Black-Hole Binaries
• Tests of general relativity from timing the double pulsar
• High-Frequency Quasi-Periodic Oscillations in black-hole binaries
• A 200-s Quasi-Periodicity Following the Tidal Disruption of a Star by a Dormant Black Hole
• The coherence of kHz quasi-periodic oscillations in the X-rays from accreting neutron stars
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Cited by in corpus (7)

• Power density spectra of modes of orbital motion in strongly curved spacetime: obtaining the observable signal
• Lower-twin-peak quasiperiodic oscillation coherence in x-ray binaries and matter stretched by tides falling onto a compact object
• Upper-twin-peak quasiperiodic oscillation in x-ray binaries and the energy from tidal circularization of relativistic orbits
• Twin peak HF QPOs as a spectral imprint of dual oscillation modes of accretion tori
• Temperature oscillations of a gas in circular geodesic motion in the Schwarzschild field
• Evidences of an innermost stable bound orbit predicted by general relativity from the amplitude of the twin-peak quasi-periodic oscillations
• Temperature oscillations of a gas moving close to circular geodesic in Reissner-Nordström spacetime