Quasi-periodic oscillations in luminous accretion discs

Abstract

Time-dependent evolution of radial pulsational instabilities in luminous accretion discs around neutron stars are analysed with a one-dimensional hydrodynamic code. In geometrically thin and optically thick accretion discs, radial oscillations are overstable to axisymmetric perturbations, as was first found by Kato S. (1978, Mont. Roy. Not. ast. Soc., 185) by linear analysis. It is due to a mechanism similar to the e mechanism in stellar pulsation. It is found that this instability induces large amplitude oscillations (more than 100 per cent) in accretion rates and small modulations (a few per cent) in temperature and surface density in the inner part of the disc, both with local Keplerian frequencies.