The origins and impact of outflow from super-Eddington flow

Abstract

Abstract It is widely believed that super-Eddington accretion flow can produce powerful outflow, but where does this originate and how much mass and energy are carried away in which directions? To answer these questions, we perform a new large-box, two-dimensional radiation hydrodynamic simulation, paying special attention lest the results should depend on the adopted initial and boundary conditions. We achieve a quasi-steady state at an unprecedentedly large range, r = 2–600rS (with rS being the Schwarzschild radius), from the black hole. The accretion rate onto the central 10 M⊙ black hole is $\dot{M}_{\rm BH} \sim 180 L_{\rm Edd}/c^{2}$, whereas the mass outflow rate is ${\dot{M}}_{\rm outflow} \sim 24 L_{\rm Edd}/c^2$ (where LEdd and c are the Eddington luminosity and the speed of light, respectively). The ratio ${\dot{M}}_{\rm outflow}/{\dot{M}}_{\rm BH} \sim 0.14$ is much less than previously reported. By careful inspection we find that most of the outflowing gas reaching the outer boundary originates from the region at R ≲ 140rS, while gas at 140–230rS forms failed outflow. Therefore, significant outflow occurs inside the trapping radius ∼450rS. The mechanical energy flux (or mass flux) reaches its maximum in the direction of ∼15° (∼80°) from the rotation axis. The total mechanical luminosity is Lmec ∼ 0.16LEdd, while the isotropic X-ray luminosity varies from $L_{\rm X}^{\rm ISO}\sim 2.9 L_{\rm Edd}$ (for a face-on observer) to ∼2.1LEdd (for a nearly edge-on observer). The power ratio is $L_{\rm mec}/L_{\rm X}^{\rm ISO}\sim 0.05$–0.08, in good agreement with observations of ultra-luminous X-ray sources surrounded by optical nebulae.