On the Origin of the Ultra-high Energy Cosmic-rays

Although their astrophysical sources remain a mystery, new measurements brought by large air shower experiments, such as the Pierre Auger Observatory and Telescope Array, have radically improved our knowledge of the ultra-high energy cosmic-rays (UHECRs). The recent report of a large scale "dipole" anisotropy, at 6 sigma significance level, has been a breakthrough in cosmic-ray physics. I will present this new observational result and discuss its possible interpretations. In particular, I will show how the extragalactic cosmic ray anisotropy  depends on the size of the cosmic ray observable universe, which is set by an interplay between diffusion in extragalactic magnetic fields and interactions with the photon backgrounds. I will show that the dipole anisotropy can be understood as a manifestation of local inhomogeneities in the large scale structure, when the effect of the magnetic field of our Galaxy is taken into account.