The X-ray ribs within the cocoon shock of Cygnus A

Abstract

We use new and archival Chandra observations of Cygnus A, totalling ∼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 Xrays 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 × 10 10 M . 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.

Detection of non-thermal X-ray emission in the lobes and jets of Cygnus A

“…The inner background regions B3 and B4 are just on the edge of the bright, rib-like structures extending outward from the AGN. Duffy et al (2018) suggest that these rib-like structures are a result of the destruction of the cool core during initial passage of the radio jet. Thermal plasma from the cool core would then be pushed into a cylindrical rib-like shape by backflow antiparallel to the direction of the jet.…”

“…Cygnus A (hereafter Cyg A) is a FRII radio galaxy (Fanaroff & Riley 1974). Its extreme radio brightness (Stockton & Ridgway 1996) made it one of the first objects of such type to be discovered.…”

“…In this paper we use 1.8 Ms of new Chandra observations, combined with 200ks of archival observations, to analyse the emission from the lobes and X-ray jets of Cyg A. Complementary results for the inner gas structure and outer lobe shocks appear in Duffy et al (2018) and Snios et al (2018), respectively. We compare different models for the lobe and jet emission and constrain their parameters.…”

Three-dimensional simulations of X-ray cavities inflated by radio galaxies

“…A new result is the appearance of a rib cage in soft X-rays which may be related to the structure found in Cygnus A as presented in detail from Chandra observations (Duffy et al 2018). We have only considered thermal X-ray emission in this work and so have investigated the shape of cavities.…”

“…Enhanced X-ray structure within the Cygnus A thermal cocoon has been identified by Smith et al (2002) as belts. With Chandra data, the description was refined to cross-cutting thick ribs which appear to be wrapped on the inside of an ellipsoidal shell (Duffy et al 2018). It is certainly reasonable to associate the observed ribs with the rib cage which occurs naturally in these simulations with the minimum of necessary ingredients.…”