Optically Thick Outflows of Supercritical Accretion Discs: Radiative Diffusion Approach

Highly supercritical accretion discs are probable sources of dense optically thick axisymmetric winds. We introduce a new approach based on diffusion approximation radiative transfer in a funnel geometry, and obtain an analytical solution for the energy density distribution inside the wind, assuming that all of the mass, momentum and energy are injected well inside the spherization radius. This allows us to derive the spectrum of the emergent emission for various inclination angles. We show that self-irradiation effects play an important role in altering the temperature of the outcoming radiation by about 20%, and the apparent X-ray luminosity by a factor of 2-3. The model has been successfully applied to two ULXs. The basic properties of the high ionization HeII-regions found around some ULXs are also easily reproduced in our models.