Stochastic modeling of kHz quasi-periodic oscillation light curves

¹ Chip Computers Consulting s.r.l., Viale Don L. Sturzo 82, S. Liberale di Marcon, 30020 Venice, Italy e-mail: robertovio@tin.it
² Max Planck Institut für Astrophysik, K. Schwarzschild str. 1, 85748 Garching b. München, Germany e-mail: pao@mpa-garching.mpg.de
³ INAF – Osservatorio Astronomico di Trieste via Tiepolo 11, 34131 Trieste, Italy e-mail: andreani@ts.astro.it
⁴ Department of Informatics and Mathematical Modelling, Technical University of Denmark, Richard Petersens Plads, 2800 Kgs. Lyngby, Denmark e-mail: hm@imm.dtu.dk
⁵ Department of Informatics and Mathematical Modelling, Technical University of Denmark, Richard Petersens Plads, 2800 Kgs. Lyngby, Denmark e-mail: rvo@imm.dtu.dk

Received: 28 October 2005
Accepted: 10 February 2006

Abstract

Aims.Kluźniak & Abramowicz explain the high frequency, double peak, “3:2” QPOs observed in neutron star and black hole sources in terms of a non-linear parametric resonance between radial and vertical epicyclic oscillations of an almost Keplerian accretion disk. The 3:2 ratio of epicyclic frequencies occurs only in strong gravity. Recently, a simple model incorporating their suggestion was studied analytically: the result is that a small forcing may indeed excite the parametric 3:2 resonance. However, no explanation has been provided on the nature of the forcing which is given an “ad hoc” deterministic form.

Methods.In the present paper the same model is considered. The equation are numerically integrated, dropping the ad hoc forcing and adding instead a stochastic term to mimic the action of the very complex processes that occur in accretion disks as, for example, MRI turbulence.

Results.We demonstrate that the presence of the stochastic term is able to trigger the resonance in epicyclic oscillations of nearly Keplerian disks, and it influences their pattern.