Cluster mergers are known to drive strong shocks into the
intracluster medium and generate turbulence. These shocks and
turbulence accelerate relativistic particles, compress magnetic fields
and heat the intracluster medium. At the same time, the cluster merger
results in a transient boost of the cluster X-ray luminosity and SZ
effect.
A clear observational connection appears to exist between
mergers and the presence of large regions of diffuse synchrotron
emission leading to the potential use of these radio signatures as a
merge-o-meter for large cluster samples. Unfortunately, we still do
not understand the details of the particle acceleration
mechanism(s).
In order to better understand the processes at work, we
have undertaken a detailed radio and X-ray study of the well known
merging cluster Abell 2256. The radio maps reveal a wealth of total
intensity and polarization structure within this system including
highly polarized Mpc scale radio relics, a Mpc scale radio halo and
numerous steep spectrum synchrotron filaments with lengths of order
200 kpc. Spectral index maps reveal spectral gradients across the
relics and suggest the presence of a Mach 2.6 shock near the
north-west boundary of the relics. XMM-Newton pressure maps show a low
pressure core co-incident with the radio halo emission, while
temperature maps reveal two cold fronts with similar directions of
motion.
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