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Astron. Astrophys. 323, L5-L8 (1997)

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Letter to the Editor

Rotational splitting effect in neutron star QPOs

L. Titarchuk 1, 2 and A. Muslimov 1

1 Laboratory for High Energy Astrophysics, Goddard Space Flight Center, Greenbelt, MD 20771, USA
2 George Mason University/CSI, Fairfax, VA 22030, USA

Received 24 April 1997 / Accepted 6 May 1997


We explain the peak spacing in the power spectra of millisecond variability detected by the Rossi X-ray Timing Explorer (RXTE) in the X-ray emission from the LMXBs (Sco X-1, 4U1728-34, 4U1608-522, 4U1636-536, etc) in terms of the rotational splitting of an intrinsic frequency (which is of order of the local Keplerian frequency) caused by an accretion disk. We calculate this effect and demonstrate that there is a striking agreement with the observational data. We show that the observed discrete frequencies ranging from 200 to 1200 Hz can be described by a whole set of overtones. For higher overtones (lower frequencies, [FORMULA] 100 Hz) the ratio between frequencies is determined by the quantum numbers alone. We suggest that a similar phenomena should be observed in Black Hole (BH) systems for which the QPO (quasi-periodic oscillation) frequency should be inversely proportional to the mass of the compact object. For BH systems the characteristic frequency of oscillations should therefore be a factor of 5-10 less than for a neutron star system.

Key words: Accretion: disk – binaries: LMXBs – X-Rays: QPOs

Send offprint requests to: L. Titarchuk

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998