Multiple density discontinuities in the merging galaxy cluster CIZA
  J2242.8+5301
  CIZA J2242.8+5301, a merging galaxy cluster at z=0.19, hosts a double-relic
system and a faint radio halo. Radio observations at frequencies ranging from a
few MHz to several GHz have shown that the radio spectral index at the outer
edge of the N relic corresponds to a shock of Mach number 4.6+/-1.1, under the
assumptions of diffusive shock acceleration of thermal particles in the test
particle regime. Here, we present results from new Chandra observations of the
cluster. The Chandra surface brightness profile across the N relic only hints
to a surface brightness discontinuity (<2-sigma detection). Nevertheless, our
reanalysis of archival Suzaku data indicates a temperature discontinuity across
the relic that is consistent with a Mach number of 2.5+/-0.5, in agreement with
previously published results. This confirms that the Mach number at the shock
traced by the N relic is much weaker than predicted from the radio. Puzzlingly,
in the Chandra data we also identify additional inner small density
discontinuities both on and off the merger axis. Temperature measurements on
both sides of the discontinuities do not allow us to undoubtedly determine
their nature, although a shock front interpretation seems more likely. We
speculate that if the inner density discontinuities are indeed shock fronts,
then they are the consequence of violent relaxation of the dark matter cores of
the clusters involved in the merger.
