Sensibility of the Pierre Auger Observatory to Large Scale Anisotropies

We study the angular power spectrum estimate in order to search for large-scale anisotropies in the arrival directions distribution of the highest-energy cosmic rays. We show that this estimate can be performed even with a coverage of the sky going to zero in some part of the sky. The recovered power spectrum is equivalent to the full sky one at the condition that the anisotropies are stationnary over the sphere. If this is not the case, the recovered power spectrum is only valid for the observed region. We apply the method to simulations of the Pierre Auger Observatory, reconstructing an input power spectrum with the Southern site only and with both Northern and Southern ones. At last, we show the improvement that the full-sky Observatory brings to test an isotropic distribution, and we discuss the sensibility of the Pierre Auger Observatory to large-scale anisotropies.