Mini radio lobes in AGNs core illumination and their hadronic gamma-ray afterlight

TL;DR

This paper models the gamma-ray spectra of mini radio lobes in active galaxies, predicting distinct hadronic features that could be observed with future telescopes, enhancing understanding of particle acceleration in AGN cores.

Contribution

It introduces a detailed hadronic model for mini radio lobes, predicting specific gamma-ray spectral features and the conditions for radio-dark gamma-ray lobes.

Findings

Two hadronic bumps in gamma-ray spectra: MeV proton synchrotron and GeV secondary electron/positron synchrotron.

Radio-dark gamma-ray lobes are predicted when particle injection is short-lived.

Future CTA observations could detect these gamma-ray signatures.

Abstract

Recent radio observations reveal the existence of mini radio lobes in active galaxies with their scales of $\sim 10 {\rm pc}$. The lobes are expected to be filled with shock accelerated electrons and protons. In this work, we examine the photon spectra from the mini lobes, properly taking the hadronic processes into account. We find that the resultant broadband spectra contain the two distinct hadronic bumps in $\gamma$-ray bands, i.e., the proton synchrotron bump at $\sim$ MeV and the synchrotron bump at $\sim$ GeV due to the secondary electrons/positrons produced via photo-pion cascade. Especially when the duration of particle injection is shorter than the lobe age, radio-dark $\gamma$-ray lobes are predicted. The existence of the $\gamma$-ray lobes could be testable with the future TeV-$\gamma$ telescope {\it CTA}.