Magnetic fields and shock waves in cluster outskirts
  Both, X-ray and radio observations, are beginning to probe regions in galaxy
clusters close to the virial radius. These are particularly interesting regions
as they are (i) crucial for the thermal evolution of the intra-cluster medium
and (ii) they host plasmas under conditions that are poorly understood.
Recently discovered giant radio relics in the galaxy cluster CIZA J2242.8+5301
provide unprecedented evidence for particle acceleration in cluster outskirts.
We will discuss some of the intriguing puzzles that surround these relics. The
polarisation of the radio emission yields information about the topology of
magnetic fields in these shock waves. Here we report on MHD simulations that
highlight some problems about the origin of these magnetic fields.
