|dc.description.abstract||Some active galactic nuclei (AGNs) are strong sources of non-thermal radiation. It
is expected that this radiation is produced in collimated outflows of plasma moving
with relativistic speeds, the so-called jets. The non-thermal radiation from AGN jets
extends over the entire electromagnetic spectrum, i.e. from the radio band to the very
high energy gamma-rays. This radiation is strongly variable in every energy range. The repro-
duction of these properties of radiation with theoretical models allows us to understand
processes and conditions occurring in AGN jets.
The AGN jets have been the subject of extensive research for several decades.
However, some fundamental questions still remain unanswered. The study of the AGN
jets can give the answers to such basic questions as: How are the non-thermal particles
accelerated inside the AGN jets? Where are the high energy γ-rays produced? What
is the type of particles responsible for the non-thermal radiation?
Most commonly, the non-thermal radiation from AGN jets is modeled with one-
zone homogeneous lepton model. In such a model, the emission region is approximated
by a spherical blob. This blob moves along the jet with relativistic speed. Such model
assumes that the conditions inside the blob are constant and homogeneous. The evident
advantage of this model is the fact that it is determined by only a few free parameters.
However, the observed spectral details and the complex temporal behaviors require
more sophisticated models.
For example, the one-zone synchrotron self-Compton model is not able to explain
the persistent emission from AGN jets. Some AGNs are observed in a low activity state
lasting for months. This persistent emission is observed also in the very high energy gamma-
ray range. In such a long period of time, the parameters in the moving emission region
should change significantly. In this context, I propose the stationary and inhomogeneous
jet model. The parameters in the model change with the distance from the jet base.
In contrast to the one-zone model, I approximate the emission region with a parsec-
scale cone which better describes the shape of AGN jets measured with the radio
telescopes. Due to the elongated shape of the jet, I take into account the non-locally
produced photons when calculating the inverse Compton process. The equilibrium state
of particles in the jet is obtained by the dedicated generation method. My approach
provides a unique tool for modeling of the jets in the persistent, low-activity emission
1The results of the commonly used emission models of AGN jets are inconsistent with
the unification model of AGNs. The unification model assumes that the radio galaxies
are counterparts of blazars observed at large angles. Whereas, the modeling of radio
galaxies requires different parameters than the modeling of blazar type of AGNs. I show
that the spectra of both, radio galaxies and blazars, considered in this thesis can be
obtained in terms of the unified model. For this purpose, I develop the two-component
jet model, in which fast-moving plasma, close to the jet axis, is surrounded by slower
plasma. In contrast to previous models of this type, I take into account the strong
interrelation between different jet components in the calculations of the equilibrium
spectrum of relativistic electrons.
In the third model, I investigate the consequences of the production of gamma-rays in
the vicinity of a super-massive black hole in blazars. Some models, supported by the
observations of the extremely fast flares, assume that the very high gamma-rays are produced
relatively close to the black hole. In the case of blazars, the jet propagates towards the
observer. Hence, these gamma-rays have to pass the jet radiation field before they escape to
the observer. These gamma-rays can be strongly absorbed initiating the inverse Compton electro-positron
pair cascades. I explore this idea in terms of the observed excess in the hard X-rays in
nearby blazar Mrk 421.||pl_PL