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Abstract

In recent years, γ-ray astronomy has made considerable progress in the exploration of the extragalactic γ-ray sky. In particular, active galaxies, whose relativistic jets/outflows are significantly inclined with respect to the lineof- sight, have revealed remarkable flaring activity at γ-ray energies. The observed rapid variability of the γ-ray emission, comparable to timescales of the light travel time across the black hole horizon, provides a strong motivation for testing radiative scenarios associated with the vicinity of the central supermassive black hole. In this doctoral study, we explore the so-called black hole magnetospheric scenario. Accordingly, strong particle acceleration may occur within the black hole magnetosphere in regions of unscreened electric fields (gaps). This can happen either at the null surface across which the charge density changes sign or at the stagnation surface which separates the inwardly from the outwardly moving matter. The acceleration of leptons is accompanied by γ-ray emission via inverse Compton scattering of the ambient (disk) soft photons as well as curvature radiation. This thesis explores the potential of these processes to account for the observed γ-ray features. By developing and studying an one-dimensional, steady model for magnetospheric particle acceleration and emission, as well as, estimating the terminal Lorentz factors of the accelerated charges and the maximum extractable gap power, we find that magnetospheric processes can be responsible for the observed, rapidly variable very-high-energy γ-ray emission in the radio galaxy M87.