Interaction in Abell 2256: the BeppoSAX view
  We present results from a spatially resolved spectral analysis of the merging cluster Abell 2256. The long integration time (135 ks) and the good spatial resolution of the MECS onboard BeppoSAX allow us to derive a new and substantially improved measurement of the temperature structure. We find that, within a central region of the cluster, where the effects of the merger are visible in the ROSAT surface brightness image, the azimuthally averaged projected temperature is remarkably flat; outside this region the projected temperature rapidly declines. The BeppoSAX data also shows clear evidence of an azimuthal temperature gradient in the 4'-8' (0.4-0.8 Mpc) radial bin, oriented in the same direction as the merger itself. Our metal abundance profile shows, for the first time, firm evidence of an abundance gradient in a rich merging cluster. Intriguingly the abundance map shows, in the SE sector, i.e. the one furthest away from the merger, a sharp factor of two drop in abundance at a radius comparable to the core radius of the cluster. A possible interpretation is that, prior to the merger event, a cooling flow had already developed in the core of the infalling subgroup, as suggested by Fabian and Daines (1991). The interaction between the substructures would have disrupted the cooling flow thereby re-heating and re-mixing the gas. As the merger in A2256 is still in a relatively early stage, the gas located on the side opposite to the merger event would still retain the low abundances associated with the intra-cluster medium (ICM) prior to the cooling flow disruption. 
Silvano Molendi, Sabrina De Grandi & Roberto Fusco-Femiano