Investigating disc-corona interaction in axisymmetric accretion disc models

Abstract

The interaction between the accretion disc and its corona plays a critical role in the energy balance and emission mechanisms in astrophysical systems such as active galactic nuclei and X-ray binaries. However, the detailed physics of disc-corona interactions, including the mechanisms driving disc evaporation and the impact of accretion rate and viscosity, remain poorly understood. Our study aims to extend the well-known disc evaporation model to investigate the disc-corona interaction in a 2D axisymmetric, time-dependent hydrodynamic model, focusing on the effects of viscosity, accretion rate, and their influence on disc evaporation, luminosity, and corona formation. We develop a hydrodynamic model consisting of a thin accretion disc, a corona, and a vacuum region. Our model is implemented in Athena++, with the gas-vacuum interface tracking algorithm to handle the vacuum regions. We perform simulations incorporating turbulent viscosity, thermal conduction, Bremsstrahlung cooling, and artificial disc cooling, starting from an adiabatic state to explore the disc-corona interaction. We demonstrate the presence of acoustic shock heating. We find that viscosity dominates the intensity of disc evaporation, that the accretion rate primarily determines the disc truncation radius and the disc luminosity, and that there may be a positive correlation between the corona luminosity and the evaporation intensity. We find the warm gas required by the warm corona model. We also compare our results with observations and simulations, and estimate the $y$-parameters to explore the potential effects of Compton cooling as well as the potential effects of the warm corona.