Discovery of an X-ray cavity near the radio lobes of Cygnus A indicating previous AGN activity

TL;DR

This study identifies an X-ray cavity near Cygnus A's radio lobes, revealing evidence of past AGN activity through multi-wavelength observations and analysis of the cavity's properties.

Contribution

It presents the discovery of a previously unknown X-ray cavity associated with Cygnus A, indicating a prior active phase of the AGN with lower energy output.

Findings

X-ray cavity filled with synchrotron plasma

Cavity age comparable to current jet age

Evidence of previous AGN activity

Abstract

Cygnus A harbours the nearest powerful radio jet of an Fanaroff-Riley (FR) class II radio galaxy in a galaxy cluster where the interaction of the jet with the intracluster medium (ICM) can be studied in detail. We use a large set of Chandra archival data, VLA and new LOFAR observations to shed new light on the interaction of the jets with the ICM. We identify an X-ray cavity in the distribution of the X-ray emitting plasma in the region south of the Cyg A nucleus which has lower pressure than the surrounding medium. The LOFAR and VLA radio observations show that the cavity is filled with synchrotron emitting plasma. The spectral age and the buoyancy time of the cavity indicates an age at least as large as the current Cyg A jets and not much larger than twice this time. We suggest that this cavity was created in a previous active phase of Cyg A when the energy output of the Active Galactic Nucleus (AGN) was about two orders of magnitude less than today.