EDP Sciences
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Volume 439, Number 2, August IV 2005
Page(s) L27 - L30
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200500151

A&A 439, L27-L30 (2005)
DOI: 10.1051/0004-6361:200500151


An explanation for the kHz-QPO twin peaks separation in slow and fast rotators

J. Pétri

Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany
    e-mail: jerome.petri@mpi-hd.mpg.de

(Received 10 June 2005 / Accepted 6 July 2005)

In this Letter we further explore the idea, suggested previously by Kluzniak and collaborators, that the high frequency QPOs may be explained as a resonant coupling between the neutron star spin and two epicyclic modes of accretion disk oscillations. We confirm result of Lee et al. (2004, ApJ, 603, L93) that the strongest response occurs when the frequency difference of the two modes equals either the spin frequency (for "slow rotators") or half of it (for "fast rotators"). New points discussed in this Letter are: (1) we suggest that the coupling is gravitational, and due to a non-axially symmetric structure of the rotating neutron star; (2) we found that two excited modes may be both connected to vertical oscillations of the disk, and that strong gravity is not needed to excite the modes.

Key words: accretion, accretion disks -- hydrodynamics -- methods: analytical -- relativity -- stars: neutron -- X-rays: binaries

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