ROSAT PSPC observations of Cygnus-A : X-ray spectra of the cooling flow and hot spots

Abstract

We present a {\it ROSAT} Position Sensitive Proportional Counter (PSPC) observation of the powerful radio galaxy Cygnus-A. The X-ray emission in the {\it ROSAT} band is dominated by thermal emission from the hot intracluster medium of the associated cluster. Image deprojection confirms the existence of a significant cluster cooling flow with total mass deposition rate of $\sim 250\,{\rm M}_\odot\,{\rm yr}^{-1}$ and a (Hubble time) cooling radius of $\sim 180$\,kpc. Spectral data show the gradient in the emission-weighted mean temperature with the temperature decreasing towards the centre of the cluster. We also find signatures of the radio source: in particular, we detect the X-ray emission from the western radio hot spot previously found by the {\it ROSAT} High Resolution Imager (HRI). We find the emission from the hot spot to be hard and discuss the physical implications of this result.Comment: uuencoded compressed postscript. The preprint is also available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm