Gravitational excitation of high frequency QPOs

Abstract

We discuss the possibility that high-frequency QPOs in neutron-star binary systems may result from forced resonant oscillations of matter in the innermost parts of the accretion disc, excited by gravitational perturbations coming from asymmetries of the neutron star or from the companion star. We find that neutron-star asymmetries could, in principle, be effective for inducing both radial and vertical oscillations of relevant amplitude while the binary companion might possibly produce significant radial oscillations but not vertical ones. Misaligned neutron-star quadrupole moments of a size advocated elsewhere for explaining limiting neutron star periods could be large enough also for the present purpose.

4 pages, 1 figure; AandA Research Note

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• Timescale of twin-peak quasi-periodic oscillations and mass of accreting neutron stars
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• Confronting models for the high-frequency QPOs with Lense-Thirring precession
• Constraining models of twin peak quasi-periodic oscillations with realistic neutron star equations of state
• Twin peak HF QPOs as a spectral imprint of dual oscillation modes of accretion tori
• The impact of neutron star spin on X-ray spectra
• Constraints on kHz QPO models and stellar EOSs from SAX J1808.4-3658, Cyg X-2 and 4U 1820-30
• Appearance of innermost stable circular orbits of accretion discs around rotating neutron stars
• Black Holes Admitting Strong Resonant Phenomena
• Of Mountains and Molehills : Gravitational Waves from Neutron Stars