Probing IC/CMB Interpretation for the X-ray knots of AGN through VHE observations

TL;DR

This paper investigates whether the inverse Compton scattering of cosmic microwave background photons explains the X-ray emission from AGN jets, predicting VHE gamma-ray signals for future CTA observations to test this model.

Contribution

It extends previous IC/CMB models to predict VHE gamma-ray emission and assesses their detectability with CTA, providing a framework to test the IC/CMB interpretation.

Findings

Predicted VHE gamma-ray fluxes for selected AGN knots.

Comparison of model predictions with CTA sensitivity.

Disfavoring IC/CMB for some sources based on gamma-ray non-detections.

Abstract

Detection of hard X-ray spectrum (spectral index < 2) from the kilo-parsec scale jet of active galactic nuclei cannot be accounted to 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 IC/CMB process, the Compton spectrum often peaks at GeV energy and many sources were predicted to be the Fermi candidate sources. The absence of significant gamma ray flux from some of these galaxies by Fermi disfavored 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 IC/CMB model which can be investigated by Cherenkov Telescope Array Observatory (CTAO). The model parameters deciding the broadband spectral energy distribution are estimated using analytical approximation of the emissivity functions. The emission model is extrapolated to VHE energy and then compared with the CTAO sensitivity. For this particular study, we have selected 18 knots with harder X-ray spectrum and for which the IC/CMB model for X-ray emission was suggested.