Speaker
Description
We explore the influence of non-geodesic pressure forces that are present in an accretion disk on the frequencies of its axisymmetric and non-axisymmetric epicyclic oscillation modes. We discuss its implications for models of high-frequency quasi-periodic oscillations (QPOs) that have been observed in the X-ray flux of accreting black holes (BHs) and neutron stars (NSs). In particular, we discuss the implications for a model recently proposed in the context of neutron NS QPOs as a disk-oscillation-based modification of the relativistic precession model. This model provides overall better fits of the NS data and predicts more realistic values of the NS mass compared to the relativistic precession model. It also implies a significantly higher upper limit on the microquasar's BH spin. We show that there is an analytic formula that well reproduce the models predictions on the QPO frequencies. Our simple formula may be used along with the observed QPO frequencies to estimate the mass and spin of compact objects.