Confinement and diffusion time-scales of CR hadrons in AGN-inflated bubbles

TL;DR

This paper investigates how cosmic-ray hadrons confined in AGN-inflated bubbles influence gamma-ray emissions in galaxy clusters, focusing on their confinement and diffusion timescales to explain observational non-detections.

Contribution

It introduces a model linking CR hadron confinement and diffusion in AGN bubbles to gamma-ray emission limits, providing new constraints on CR transport in galaxy clusters.

Findings

CR hadron confinement times are constrained by gamma-ray non-detections.

Fast CR diffusion can explain the lack of observed gamma-ray emission.

Limits on CR escape influence models of AGN feedback in galaxy clusters.

Abstract

While rich clusters are powerful sources of X-rays, gamma-ray emission from these large cosmic structures has not been detected yet. X-ray radiative energy losses in the central regions of relaxed galaxy clusters are so strong that one needs to consider special sources of energy, likely AGN feedback, to suppress catastrophic cooling of the gas. We consider a model of AGN feedback that postulates that the AGN supplies the energy to the gas by inflating bubbles of relativistic plasma, whose energy content is dominated by cosmic-ray (CR) hadrons. If most of these hadrons can quickly escape the bubbles, then collisions of CRs with thermal protons in the intracluster medium (ICM) should lead to strong gamma-ray emission, unless fast diffusion of CRs removes them from the cluster. Therefore, the lack of detections with modern gamma-ray telescopes sets limits on the confinement time of CR hadrons in bubbles and CR diffusive propagation in the ICM.