Breathing oscillations in a global simulation of a thin accretion disc

We study the oscillations in an axisymmetric, viscous, radiative, general relativistic hydrodynamical simulation of a geometrically thin disc around a non-rotating, 6.62 M-circle dot black hole. The numerical set-up is initialized with a Novikov-Thorne, gas pressure-dominated accretion disc, with an initial mass accretion rate of (m) over dot = 0.01L(Edd)/c(2) (where L-Edd is the Eddington luminosity and c is the speed of light). Viscosity is treated with the alpha-prescription. The simulation was evolved for about 1000 Keplerian orbital periods at three Schwarzschild radii (ISCO radius). Power density spectra of the radial and vertical fluid velocity components, the total (gas + radiation) mid-plane pressure, and the vertical component of radiative flux from the photosphere, all reveal strong power at the local breathing oscillation frequency. The first, second, and third harmonics of the breathing oscillation are also clearly seen in the data. We quantify the properties of these oscillations by extracting eigenfunctions of the radial and vertical velocity components and total pressure. This confirms that these oscillations are associated with breathing motion.