Probing the origin of two population electron hypotheses in large scale X-ray jet of Active Galaxies

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.