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We present an analysis of high-quality X-ray data out to the virial radiusfor the two galaxy clusters Abell 1246 and GMBCG J255.34805+64.23661 (J255) bymeans of our entropy-based SuperModel. For Abell 1246 we find that thespherically-averaged entropy profile of the intracluster medium (ICM)progressively flattens outwards, and that a nonthermal pressure componentamounting to ~20% of the total is required to support hydrostatic equilibriumin the outskirts; there we also estimate a modest value C~1.6 of the ICMclumping factor. These findings agree with previous analyses on othercool-core, relaxed clusters, and lend further support to the picture by Lapi etal. (2010) that relates the entropy flattening, the development of nonthermalpressure component, and the azimuthal variation of ICM properties to weakeningboundary shocks. In this scenario clusters are born in a high-entropy statethroughout, and are expected to develop on similar timescales a low entropystate both at the center due to cooling, and in the outskirts due to weakeningshocks. However, the analysis of J255 testifies how such a typical evolutionarycourse can be interrupted or even reversed by merging especially atintermediate redshift, as predicted by Cavaliere et al. (2011b). In fact, amerger has rejuvenated the ICM of this cluster at z~0.45 by reestablishing ahigh entropy state in the outskirts, while leaving intact or erasing onlypartially the low-entropy, cool core at the center.

SuperModel Analysis of Abell 1246 and J255: on the Evolution of Galaxy Clusters from High to Low Entropy States