ROSAT and BeppoSAX Evidence of Soft X-Ray Excess Emission in the Shapley Supercluster: A3571, A3558, A3560, and A3562

Excess soft X-ray emission in clusters of galaxies has so far been detected for sources that lie along lines of sight to very low Galactic H I column density [such as Coma, A1795, A2199, and Virgo; NH ~ (0.9-2.0) × 1020 cm-2]. We show that the cluster soft excess emission can be investigated even at higher NH, which provides an opportunity for investigating soft X-ray emission characteristics among a large number of clusters. The ROSAT Position Sensitive Proportional Counter analysis of some members of the Shapley concentration [A3571, A3558, A3560, and A3562 at NH ~ (4-4.5) × 1020 cm-2] bears evidence for excess emission in the keV band. We were able to confirm the finding for the case of A3571 by a pointed BeppoSAX observation. Within the current sample, the soft X-ray flux is again found to be consistently above the level expected from a hot virialized plasma. The data quality is, however, insufficient to enable a discrimination between alternative models of the excess low-energy flux.