Radiative Shocks around Super-Eddington Accreting Black Holes

TL;DR

This study uses 2D radiation hydrodynamic simulations to explore radiative shocks in super-Eddington accretion flows around stellar-mass black holes, revealing high luminosities, anisotropic radiation, and potential explanations for sources like SS 433 and ULXs.

Contribution

It presents the first detailed 2D radiation hydrodynamic models of radiative shocks in super-Eddington accretion flows, highlighting their observational signatures and relevance to ultraluminous X-ray sources.

Findings

Luminosity reaches ~10^{40} erg/s with anisotropic distribution.

Shock location moves inward with increasing accretion rate.

Models produce black body spectra with temperatures of 5-30 million K.

Abstract

We examine radiative standing shocks in advective accretion flows around stellar-mass black holes by 2D radiation hydrodynamic simulations, focusing on the super-Eddington accreting flow. Under a set of input flow parameters responsible for the standing shock, the shock location on the equator decreases toward the event horizon with an increasing accretion rate. The optically thin and hot gas in the narrow funnel region along the rotational axis changes gradually into a dense and optically thick state with the increasingly dense gas transported from the base of the radiative shock near the equator. As a result, the luminosity becomes as high as ~ $10^{40}$ erg $s^{-1}$, and the radiation shows a strongly anisotropic distribution around the rotational axis and then very low edge-on luminosity as ~ $10^{36}$ erg $s^{-1}$. The mass outflow rate from the outer boundary is high as ~ $10^{-5}$ and $10^{-4}$ $M_{\odot} yr^{-1}$ but most of the outflow is originated through the radial outer boundary and may be observed over a wide wind region. The models show approximately black body spectra with a temperature of $5 \times 10^{6} - 3 \times 10^{7}$ K at the vertical outer boundary surface. The radiative shock models with the super-Eddington luminosities show a possible model for the superaccretor SS 433 and Ultraluminous X-ray sources with stellar-mass black holes.