Optically Thick Outflows of Supercritical Accretion Discs: Radiative Diffusion Approach

TL;DR

This paper presents an analytical model for optically thick winds from supercritical accretion discs, accounting for radiative diffusion and self-irradiation effects, with applications to ultraluminous X-ray sources (ULXs).

Contribution

It introduces a new diffusion-based analytical approach to model dense winds from supercritical accretion discs, incorporating self-irradiation effects and applying it to ULXs.

Findings

Self-irradiation alters outflow temperature by ~20%.

X-ray luminosity can increase by a factor of 2-3 due to self-irradiation.

Model successfully explains properties of ULXs and surrounding HII regions.

Abstract

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 the mass, momentum and energy are injected well inside the spherization radius. This allows to derive the spectrum of emergent emission for various inclination angles. We show that self-irradiation effects play an important role 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 HII-regions found around some ULXs are also easily reproduced in our assumptions.