Core - Corona Model describes the Centrality Dependence of v_2/epsilon

Event by event EPOS calculations in which the expansion of the system is described by {\it ideal} hydrodynamics reproduce well the measured centrality dependence of $v_2/\epsilon_{part}$, although it has been claimed that only viscous hydrodynamics can reproduce these data. This is due to the core - corona effect which manifests itself in the initial condition of the hydrodynamical expansion. The centrality dependence of $v_2/\epsilon_{part}$ can be understood in the recently advanced core-corona model, a simple parameter free EPOS inspired model to describe the centrality dependence of different observables from SPS to RHIC energies. This model has already been successfully applied to understand the centrality dependence of multiplicities and of the average transverse momentum of identified particles.