Forced oscillations in fluid tori and quasi‐periodic oscillations

Abstract

Abstract. The kilo-Hertz Quasi-Periodic Oscillations in X-ray binaries could originate within the accretion flow, and be a signature of non-linear fluid oscillations and mode coupling in strong gravity. The possibility to decipher these systems will impact our knowledge of fundamental parameters such as the neutron star mass, radius, and spin. Thus they offer the possibility to constrain the nuclear equation of state and the rotation parameter of stellar-mass black holes. We review the general properties of these oscillations from a hydrodynamical point of view, when the accretion flow is subject to external perturbations and summarize recent results.

QPO as the Rosetta Stone for understanding black hole accretion

“…For example, difference in frequencies of the double peaked QPO in the millisecond pulsar SAX J1808.4-3658 is clearly equal to half of the pulsar spin. This suggests that the epicyclic resonance is excited by direct forcing of accretion disk oscillation modes by the neutron star spin (Lee 2005).…”

“…This is a rather difficult mathematical problem that takes time -first results are excepted this year 7 (Rebusco 2005). So far, all our published results on the cos(ω 0 t) external forcing of oscillations of tori are based on numerical simulations -both SPH (Lee 2005) and grid (Sramkova 2005).…”

Weak nonlinear coupling between epicyclic modes in slender tori

“…The resonance arises due to nonlinear coupling between the epicyclic modes. In the scenario suggested by Kluźniak & Abramowicz (2002), one mode is first excited externally, either by an external periodic forcing due to rotation of the central object (Lee et al 2004;Lee 2005) or by a stochastic forcing due to turbulence in the accretion flow (Vio et al 2006). The other mode is then continously supplied by the energy from the former one via the parametric resonance.…”