Quasi-periodic oscillations in luminous accretion discs

We examine the time-dependent evolution of radial pulsational instabilities in luminous accretion discs around neutron stars, using a one-dimensional hydrodynamic code. In geometrically thin and optically thick accretion discs, radial oscillations are overstable to axisymmetric perturbations. It is due to a mechanism similar to the ε mechanism in stellar pulsation. We find 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 in the inner part of the disc, both with local Keplerian frequencies. (author)