Probing the IC/CMB interpretation for the X-ray knots of AGNs through VHE observations

Abstract

ABSTRACT The detection of hard X-ray spectra (spectral index <2) from the kiloparsec-scale jet of active galactic nuclei cannot be accounted for by the synchrotron emission mechanism from the electron distribution responsible for the radio/optical emission. Alternate explanations are the inverse Compton scattering of cosmic microwave background photons (IC/CMB) or synchrotron emission from a second electron population. When the X-ray emission is interpreted as an IC/CMB process, the Compton spectrum often peaks at GeV energy and many sources are predicted to be Fermi candidate sources. The absence of significant gamma-ray flux from some of these galaxies by Fermi disfavours the IC/CMB interpretation of the high-energy emission. We extend this study to predict the very-high-energy (VHE) gamma-ray emission due to the IC/CMB model, which can be investigated by the Cherenkov Telescope Array Observatory (CTAO). The model parameters deciding the broad-band spectral energy distribution are estimated using an analytical approximation of the emissivity functions. The emission model is extrapolated to VHE and then compared with the CTAO sensitivity. For this particular study, we have selected 18 knots with harder X-ray spectra and for which the IC/CMB model for X-ray emission has been suggested.