THE DISTRIBUTION OF DARK MATTER IN THE A2256 CLUSTER

Using spatially resolved X-ray spectroscopy, we have determined that the X-ray emitting gas in the rich cluster A2256 is nearly isothermal to a radius of at least 0.76 h-1 Mpc, or about three core radii. These data can be used to measure the distribution of the dark matter in the cluster. We find that the total mass interior to 0.76 h-1 Mpc and 1.5 h-1 Mpc is (0.5 +/- 0.1 and 1.0 +/- 0.5) x 10(15) h-1 M. respectively where the errors encompass the full range allowed by all models that we have fit to our data. Thus the mass appropriate to the region where we have spectral information is well determined, but the uncertainties become rather large upon extrapolating beyond that region. We also find that the galaxy orbits are mildly anisotropic which may cause the beta discrepancy in this cluster.