Damping of disco-seismic C-mode oscillations at the sonic radius of discs

Abstract

ABSTRACT In a previous paper we have suggested that two-armed disc deformation excites two- or three-armed disco-seismic c-mode oscillations by three-mode resonant coupling processes. This might be one of possible causes of the QPOs observed in low-mass X-ray binaries and in black-hole sources. In another previous paper we showed that for these c-mode oscillations to be time periodic, they must satisfy some boundary conditions (regularity conditions) at the sonic point where accretion speed becomes transonic. In this paper we show that these boundary conditions acts so as to dampen the oscillations. This might be favourable for explaining why the QPOs are quasi-periodic.