  We present the results of deep Chandra and XMM-Newton X-ray imaging and
spatially-resolved spectroscopy of Abell 2256, a nearby (z=0.058) galaxy
cluster experiencing multiple mergers and displaying a rich radio morphology
dominated by a large relic. The X-ray data reveals three subclusters: (i) the
`main cluster'; (ii) the remnant of an older merger in the east of the cluster
with a ~ 600 kpc long tail; (iii) a bright, bullet-like, low-entropy infalling
system, with a large line-of-sight velocity component. The low-entropy system
displays a 250 kpc long cold front with a break and an intriguing surface
brightness decrement. Interestingly, the infalling gas is not co-spatial with
bright galaxies and the radio loud brightest cluster galaxy of the infalling
group appears dissociated from the low entropy plasma by 50 kpc in projection,
to the south of the eastern edge of the cold front. Assuming that the dark
matter follows the galaxy distribution, we predict that it is also
significantly offset from the low-entropy gas. Part of the low frequency radio
emission near the cold front might be revived by magnetic field amplification
due to differential gas motions. Using analytical models and numerical
simulations, we investigate the possibility that the supersonic infall of the
subcluster generates a large scale shock along our line-of-sight, which can be
detected in the X-ray temperature map but is not associated with any clear
features in the surface brightness distribution.
