Two-temperature accretion disks with electron—positron pairs

Abstract

We investigate two-temperature disks that contain electron-positron pairs generated by nonthermal cascading. We show the existence of a critical accretion rate both for bremsstrahlung and comptonized bremsstrahlung disks. Below the critical value, there is a unique stationary solution for the disk structure; above the critical value, there is none such. For the comptonized disk, we have derived the relations between critical accretion rate and the Shakura-Sunyaev viscosity parameter α and the energy-generation parameter ε e. For the bremsstrahlung disk, the effect of electron pairs can be neglected; for the comptonized disk, the electron-pairs can have densities as high as 10 −2 ∼ 10 0, and exert much influence on the disk structure and spectrum.