Compton‐heated Outflow from Convection‐dominated Accretion Flows

Abstract

Convection-dominated accretion flows (CDAFs) are expected to have a shallower density profile and a higher radiation efficiency compared to advection-dominated accretion flows (ADAFs). Both solutions have been developed to account for the observed properties of the low-luminosity, high-temperature X-ray sources believed to involve accretion onto massive black holes. Self-similar CDAFs also have steeper poloidal density gradients and temperatures close to the virial temperature. All these characteristics make CDAFs more capable of producing polar outflows driven by Compton heating as compared to other classical accretion disks. We investigate the conditions for producing such outflows in CDAFs and look for the mass accretion rate or, equally, the luminosity of CDAFs for which such outflows will exist. When the electron temperature saturates around 1011 K at the inner region, polar outflows are probable for 8 × 10-7 L/LE 4 × 10-5, where LE is the Eddington luminosity. Outflows are well collimated with small opening angles. The luminosity range for which outflow solutions exist is narrower for lower electron temperature flows and disappears completely for electron temperature 6 × 109 K. When the magnetic field is present, we find that outflows are possible if the magnetic field is less than from 10% to 1% of the equipartition field. We also find that outflows are more likely to be produced when the viscosity parameter α is small. The tendency for jetlike collimated outflows to result from these solutions is presumably astrophysically relevant given the high frequency of jets from active galactic nuclei.