Nonaxisymmetricg‐Mode andp‐Mode Instability in a Hydrodynamic Thin Accretion Disk

Abstract

It has been suggested that quasi-periodic oscillations of accreting X-ray sources may relate to the modes named in the title. We consider nonaxisymmetric linear perturbations to an isentropic, isothermal, unmagnetized thin accretion disk. The radial wave equation, in which the number of vertical nodes (n) appears as a separation constant, admits a wave action current that is conserved except, in some cases, at corotation. Waves without vertical nodes amplify when reflected by a barrier near corotation. Their action is conserved. As was previously known, this amplification allows the n = 0 modes to be unstable under appropriate boundary conditions. In contrast, we find that waves with n > 0 are strongly absorbed at corotation rather than amplified; their action is not conserved. Therefore, nonaxisymmetric p-modes and g-modes with n > 0 are damped and stable even in an inviscid disk. This eliminates a promising explanation for quasi-periodic oscillations in neutron star and black hole X-ray binaries.