A multiband study of Hercules A. I. ROSAT observations of the   intracluster medium
  We have made ROSAT PSPC and HRI X-ray observations to study the intracluster gas surrounding the powerful radio source Hercules A. The cluster is luminous in X-rays (L_bol = 4.8x10^37 W), and the host of the radio source is the central dominating galaxy of the cluster. The X-ray surface brightness profile is well fitted by a modified King beta model, but the cluster is elongated parallel to the radio source, especially on the scale of the radio lobes. Fits to individual quadrants give a core radius 50 per cent larger along the radio axis. Part of this elongation appears to be associated with enhanced X-ray emission superimposed on the outer radio lobes. There are no obvious depressions in the X-ray emission coincident with the radio lobes, as expected if the relativistic plasma displaces the ICM. However, we show that these depressions may be quite weak. From the surface brightness profile for the PSPC data the X-ray emission extends out to ~ 2.2 Mpc radius. In the absence of the powerful jets, we would expect a cooling flow at the centre of the cluster, but currently it must be substantially disturbed by the expansion of the radio lobes. The PSPC spectrum reveals a cool component of the ICM with 0.5 < kT < 1 keV. The central cooling time could be as low as 2 Gyr if the cool component is centrally concentrated, otherwise it is around 6 Gyr. The modelled central electron density is typical for modest cooling flows. Finally, we have detected faint X-ray emission from a compact central source. 
Nectaria A. B. Gizani (Institute of Astronomy and Astrophysics,   National Observatory of Athens, Greece) and J. P. Leahy (U...