Interaction in Abell 2256: The BeppoSAX view

We present results from a spatially resolved spectral analysis of the mergi ng cluster Abell 2256. The long integration time (135 ks) and the good spat ial resolution of the Medium-Energy Concentrator/Spectrometer on board Bepp oSAX allow us to derive a new and substantially improved measurement of the temperature structure. We find that, within a central region of the cluste r, where the effects of the merger are visible in the ROSAT surface brightn ess image, the azimuthally averaged projected temperature is remarkably fla t; outside this region, the projected temperature rapidly declines. The Bep poSAX data also show 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 southeast sector, i.e., the one farthest aw ay from the merger, a sharp factor of 2 drop in abundance at a radius compa rable 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 & Daines. The interactio n between the substructures would have disrupted the cooling flow, thereby reheating and remixing the gas. Since the merger in A2256 is still in a rel atively early stage, the gas located on the side opposite the merger event would still retain the low abundances associated with the intracluster medi um prior to the cooling flow disruption.