Twin peak quasi-periodic oscillations as signature of oscillating cusp torus

Abstract

Abstract Serious theoretical effort has been devoted to explain the observed frequencies of twin-peak quasi-periodic oscillations (HF QPOs) observed in low-mass X-ray neutron star binaries. Here we propose a new model of HF QPOs. Within its framework we consider an oscillating torus with cusp that changes location r0 of its centre around radii very close to innermost stable circular orbit. The observed variability is assigned to global modes of accreted fluid motion that may give strong modulation of both accretion disc radiation and the accretion rate. For a given space–time geometry, the model predicts that QPO frequencies are function of single parameter r0. We illustrate that the model can provide fits of data comparable to those reached by other models, or even better. In particular, it is compared to relativistic precession model. Moreover, we also illustrate that the model consideration is compatible with consideration of models of a rotating neutron star in the atoll source 4U 1636−53.