  Combining XMM-Newton and Chandra data, we have performed a detailed study of
Abell 3558. Our analysis shows that its dynamical history is more complicated
than previously thought. We have found some traits typical of cool core
clusters (surface brightness peaked at the center, peaked metal abundance
profile) and others that are more common in merging clusters, like deviations
from spherical symmetry in the thermodynamic quantities of the ICM. This last
result has been achieved with a new technique for deriving temperature maps
from images. We have also detected a cold front and, with the combined use of
XMM-Newton and Chandra, we have characterized its properties, such as the speed
and the metal abundance profile across the edge. This cold front is probably
due to the sloshing of the core, induced by the perturbation of the
gravitational potential associated with a past merger. The hydrodynamic
processes related to this perturbation have presumably produced a tail of lower
entropy, higher pressure and metal rich ICM, which extends behind the cold
front for about 500 kpc. The unique characteristics of A3558 are probably due
to the very peculiar environment in which it is located: the core of the
Shapley supercluster.
