Supercritical accretion and ULXs

AbstractSupercritical (or super‐Eddington) accretion seems to occur in various black hole objects, including microquasars and ultra‐luminous X‐ray sources. We, here, elucidate the theory of supercritical accretion flow based on our two‐dimensional (2‐D) global radiation‐hydrodynamic (RHD) and radiation‐magnetohydrodynamic (RMHD) simulations. We first confirm that there is practically no limit to the accretion rate onto black holes. We then discuss several noteworthy observable features of the supercritical flow; that is, mild beaming, relativistic, collimated outflow, and inverse‐Compton scattering spectra by optically thick outflow. For face‐on observers the maximum apparent (isotropic) luminosities of ∼22LE (with L E being the Eddington luminosity) can be achieved for the mass supply rate of ∼50LE/c2. Even larger isotropic luminosities are possible for higher mass supply rates. For edge‐on observers, conversely, the apparent luminosity will be much less. It will be even lower, if the the innermost bright part of the disk is obscured by the outer part. High velocity (>0.5c) jet accelerated by radiation‐pressure force and collimated by Lorentz force is also expected. We expect large kinetic luminosity, ∼0.1LE, and high mass outflow rate, ∼10LE/c2. This may account for large ionizing nebulae around ULXs (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)