Chandra and XMM-Newton observations of A2256: cold fronts, merger
  shocks, and constraint on the IC emission
  We present the results of deep Chandra and XMM-Newton observations of a
complex merging galaxy cluster Abell 2256 (A2256) that hosts a spectacular
radio relic (RR). The temperature and metallicity maps show clear evidence of a
merger between the western subcluster (SC) and the primary cluster (PC). We
detect five X-ray surface brightness edges. Three of them near the cluster
center are cold fronts (CFs): CF1 is associated with the infalling SC; CF2 is
located in the east of the PC; and CF3 is to the west of the PC core. The other
two edges at cluster outskirts are shock fronts (SFs): SF1 near the RR in the
NW has Mach numbers derived from the temperature and the density jumps,
respectively, of $M_T=1.62\pm0.12$ and $M_\rho=1.23\pm0.06$; SF2 in the SE has
$M_T=1.54\pm0.05$ and $M_\rho=1.16\pm0.13$. In the region of the RR, there is
no evidence for the correlation between X-ray and radio substructures, from
which we estimate an upper limit for the inverse-Compton emission, and
therefore set a lower limit on the magnetic field ($\sim$ 450 kpc from PC
center) of $B>1.0\ \mu$G for a single power-law electron spectrum or $B>0.4\
\mu$G for a broken power-law electron spectrum. We propose a merger scenario
including a PC, an SC, and a group. Our merger scenario accounts for the X-ray
edges, diffuse radio features, and galaxy kinematics, as well as projection
effects.
