The XMM Cluster Outskirts Project (X-COP)
  Galaxy clusters are thought to grow hierarchically through the continuous
merging and accretion of smaller structures across cosmic time. In the local
Universe, these phenomena are still active in the outer regions of massive
clusters ($R>R_{500}$), where the matter distribution is expected to become
clumpy and asymmetric because of the presence of accreting structures. We
present the XMM-Newton Cluster Outskirts Project (X-COP), which targets the
outer regions of a sample of 13 massive clusters
($M_{500}>3\times10^{14}M_\odot$) in the redshift range 0.04-0.1 at uniform
depth. The sample was selected based on the signal-to-noise ratio in the Planck
Sunyaev-Zeldovich (SZ) survey with the aim of combining high-quality X-ray and
SZ constraints throughout the entire cluster volume. Our observing strategy
allows us to reach a sensitivity of $3\times10^{-16}$ ergs cm$^{-2}$ s$^{-1}$
arcmin$^{-2}$ in the [0.5-2.0] keV range thanks to a good control of systematic
uncertainties. The combination of depth and field of view achieved in X-COP
will allow us to pursue the following main goals: i) measure the distribution
of entropy and thermal energy to an unprecedented level of precision; ii)
assess the presence of non-thermal pressure support in cluster outskirts; iii)
study the occurrence and mass distribution of infalling gas clumps. We
illustrate the capabilities of the program with a pilot study on the cluster
Abell 2142.
