Radiative-hydrodynamical simulations of accretion disk coronae

We have developed an algorithm that will carry out detailed, two-dimensional, fully self-consistent radiative-hydrodynamical simulations of accretion disk coronae in X-ray-luminous compact sources. The calculation reported here, for an accreting neutron star radiating at 0.5 times the Eddington luminosity, reveals several striking features. (1) The corona is comprised of two main regions - an inner (r ≲1 × 10⁸ cm) highly dynamic portion whose vertical structure varies cyclically on a dynamical time scale (∼0.2 s), and an outer, more stable zone in which the evaporated plasma rises to form a "sheath" that gradually merges into a wind at large radii. (2) The coronal structure shows a density inversion (due to the ram pressure support of the ionized flow) that contrasts sharply with the Gaussian profiles of earlier hydrostatic models. (3) Interestingly, flow velocities as high as a few × 10⁹ cm s^-1 are not uncommon in portions of the corona. We discuss the relevance of this point to the large measured width of the emission features seen in low-mass X-ray binaries and the Galactic black hole candidates.