| dc.description.abstract | Active Galactic Nuclei (AGN) are one of the most energetic sources in the universe. These
galaxies host a supermassive black hole at their centre. Most of the AGNs are observed to
host a relativistic jet that can extend up to kilo-parsec/mega-parsec scales and is powered
by supermassive black holes. In this thesis, we study the hard X-ray emission from the
kilo-parsec scale jet of active galactic nuclei, which cannot be attributed to the synchrotron
emission mechanism from the electron distribution responsible for the radio/optical emissions.
Alternatively, two interpretations are proposed; the inverse Compton scattering of cosmic
microwave background photons by the relativistic synchrotron-emitting electrons in the jet
(IC/CMB model) or synchrotron emission from a second electron population. The IC/CMB
interpretation of X-ray emission, on the other hand, suggests significant gammaray emission
from the kilo-parsec scale jets. However, the non-detection of gamma-ray flux from these
galaxies by Fermi/LAT disfavors this interpretation rather advocates the second population
of electrons as a possible cause for X-ray emission. Here, we explore the possible origin of
the second population, particularly considering a scenario where the high-energy electrons
from the sites of particle acceleration advect into the jet medium. This advected electron
distribution is significantly different from the accelerated electron distribution and satisfies
the requirements of the second electron population. We find that the multi-spectral component
(MSC) emission from these large-scale AGN jets can be explained by the synchrotron emission
from the accelerated and the advected electron distribution. Nevertheless, the IC/CMB model
was accepted for sources at higher redshifts due to the increase in CMB energy density with
redshift. Recent gamma-ray flux upper limits of high redshift sources, namely J1510+5702
and J1421-0643, do not comply with the IC/CMB predictions. Application of the electron
acceleration and advection models to these sources can interpret their MSC jet emission.
Irrespective of the Fermi results, further stringent constraints on the IC/CMB model can
be put forth from the very high energy (VHE) observations. The IC/CMB emission model
is extrapolated to VHE and then compared with the sensitivity of the upcoming Cherenkov
Telescope Array Observatory. We find candidate sources whose IC/CMB spectrum falls within
its detection threshold, and future observations by CTAO have the potential to validate the
high-energy emission process from the large-scale AGN jet. | en_US |
