The intracluster gas around Cygnus A.

Einstein Observatory X-ray observations show that the radio source Cygnus-A lies at the centre of about 10¹⁴M_sun; of hot gas. In one direction this gas extends to over 1 Mpc from the radio source, a size comparable with previously observed large X-ray clusters. Gas out to a radius of 125 kpc has a cooling time of less than a Hubble time leading to a cooling flow of about 90 M_sun;yr^-1. The hot gas has an r^-1 density profile giving an age of less than 2×10⁷yr for a constant power input from the beam. The hotspot advance speed is found to be greater than 0.011 c, using recently published estimates of the pressure in the radio hotspots. Present X-ray observations are not able to detect the shocked gas confining the radio plasma.