Critical accretion disk

For a supercritical accretion regime, we propose a critical accretion disk, where the mass-accretion rate is regulated just at the critical rate with the help of wind mass-loss. We first derive a critical radius, inside of which the standard picture is violated, using the condition that the radiative force is balanced by the gravity in the vertical direction. The critical radius r(cr) is found to be r(cr) = (9root3sigma(T)/16pi cm(p))M-input = 1.95(M-input/M-crit)r(g), where M-input is the mass-accretion rate at the outer edge of the disk, A M-crit the critical accretion rate, and r(g) the Schwarzschild radius of the central object. Outside of this critical radius, the disk is in a radiation-pressure dominated standard state, while inside this radius the disk is in a critical state, where the excess mass is expelled by wind and the accretion rate is kept to be just at the critical rate at any radius inside r(cr). In such a critical accretion disk, the disk thickness is H similar to (1/6root3)r and the surface temperature is or T-4 similar to (2/3root3)L-E/4pir(2), where L-E is the Eddington luminosity. The total disk luminosity becomes L-disk similar to (2/3vroot3)[ln(r(cr)/r(in)) + 1]L-E, where r(in) is the inner radius. We apply the present model to microquasars and narrow-line Seyfert I galaxies, which are supposed to be under supercritical accretion.