Hot one-temperature accretion flows around black holes

We describe hot, optically thin solutions for one-temperature accretion disks around black holes. We include cooling by synchrotron, bremsstrahlung, and Comptonization. Our solutions are thermally and viscously stable, with gas temperatures on the order of T ∼ 10⁹-10^10.7 K. The thermal stability is a direct result of the inclusion of synchrotron cooling. The new solution branch is related to the advection-dominated solution for a two-temperature gas, described by Narayan & Yi (1995b). It is present only for mass accretion rates less than some critical M_crit, which depends on the radius R and viscosity parameter α. The solutions are advection dominated for extremely low values of Ṁ. However, for a range of intermediate accretion rates, the new solutions are both hot (T ∼ 10¹⁰ K) and cooling dominated. Because of this new feature, one-temperature solutions are significantly more luminous than the corresponding two-temperature solutions at the same M. The radial profile of the new solutions is unusual. The inner parts of the flow are cooling-dominated and have a disklike geometry, while the outer parts are fully advection-dominated and nearly quasispherical.