Accretion-Disk Corona Advected by External Radiation Drag I.

Abstract

We examined an accretion-disk corona (β-corona) which is dynamically driven via the radiation drag exerted by a central luminous source and the accretion disk, itself. We adopted the standard α-disk as the disk model. We considered a geometrically thin and optically thin corona and ignored any motion such as wind. When the central source is sufficiently luminous, the specific angular momentum of the corona gas is lost by the radiation drag of the radiation field produced by the central source. As a result, the rotation velocity of the corona gas becomes smaller than a Keplerian one, and the corona gas is advected inward on a dynamical timescale. This new picture concerning the accretion-disk corona — a dynamical disk corona — is a rather universal one. When the accretion disk is luminous, on the other hand, the corona gas tends to corotate with the underlying disk by radiation drag of the radiation field produced by the α -disk. As a result, the advection of the corona gas is suppressed (this is the case of the traditional picture of a stationary disk corona). In addition, the emission-line profiles expected from these advected disk corona can be calculated for a wide variety of parameters. The line profiles are generally double peaked. The separation of two peaks depends on the brightness of the central source as well as the size of the emitting regions. When the central source is brighter, the separation of two peaks becomes smaller.