Gamma-rays from the IC $e^{\pm }$ pair cascade in the radiation field of an accretion disk: Application to CenA

Abstract

The very short time scale variability of TeV $\gamma$-ray emission from active galaxies suggests that the acceleration process of particles and the production of primary $\gamma$-rays likely occurs relatively close to the accretion disk. We calculate the $\gamma$-ray spectra produced in an Inverse Compton $e^{\pm }$ pair cascade initiated by primary $\gamma$-rays which are injected close to the surface of the accretion disk. Possible synchrotron energy losses of secondary cascade $e^{\pm }$ pairs are also taken into account. Since the soft radiation field is anisotropic, the resulting $\gamma$-ray spectra strongly depend on the observation angle. We investigate their basic properties for different parameters describing such a model. The model is applied to the misaligned blazar Cen A recently detected in the TeV $\gamma$-rays. We conclude on the site of the $\gamma$-ray emission region in Cen A based on the comparison of the model with the observations of this source in the GeV-TeV energy range.

7 pages, 4 figures, accepted for publication in MNRAS

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• GeV-TeV gamma-rays produced by electrons in the kpc scale jet as a result of comptonization of the inner jet emission
• Time dependent gamma-ray production in the anisotropic IC $e^{\pm }$ pair cascade initiated by electrons in active galaxies
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