The X-ray Ribs Within the Cocoon Shock of Cygnus A

TL;DR

This study uses extensive Chandra X-ray observations to analyze the temperature and distribution of rib-like gas structures within Cygnus A's cocoon shock, revealing asymmetries and their likely origin from cluster core debris.

Contribution

It provides new insights into the temperature structure, asymmetry, and origin of gas within Cygnus A's cocoon shock, based on detailed X-ray analysis.

Findings

Gas is dominated by thermal emission at ~4 keV.

Asymmetry in temperature gradient with cooler southwestern region.

Gas mass estimated at approximately 2×10^{10} solar masses.

Abstract

We use new and archival Chandra observations of Cygnus A, totalling $\sim$1.9 Ms, to investigate the distribution and temperature structure of gas lying within the projected extent of the cocoon shock and exhibiting a rib-like structure. We confirm that the X-rays are dominated by thermal emission with an average temperature of around 4 keV, and have discovered an asymmetry in the temperature gradient, with the southwestern part of the gas cooler than the rest by up to 2 keV. Pressure estimates suggest that the gas is a coherent structure of single origin located inside the cocoon, with a mass of roughly $2\times10^{10} M_{\odot}$. We conclude that the gas is debris resulting from disintegration of the cool core of the Cygnus A cluster after the passage of the jet during the early stages of the current epoch of activity. The 4 keV gas now lies on the central inside surface of the hotter cocoon rim. The temperature gradient could result from an offset between the centre of the cluster core and the Cygnus A host galaxy at the switch-on of current radio activity.