Escape of TeV gamma rays from anisotropic thermal photon fields in active galactic nuclei

Abstract

We calculate the optical depth of TeV γ-rays that result from the anisotropic IR-UV thermal radiation of the α-disk model proposed by Shakura & Sunyaev. Our calculations yield the dependences of the optical depth of high-energy γ-rays on the disk parameters (i.e., α, M8, and M26), photon energy, and Φ, the angle between the propagation direction and the rotation axis of the accretion disk. Our results indicate that TeV γ-rays can escape more easily from the central engine with lower values of & (≲0.01) and Φ. We conclude that the optical depth of TeV γ-rays in the anisotropic thermal radiation field places certain constraints on the possible values of the parameter a and the position of the emission region. © 1997. The American Astronomical Society. All rights reserved.