Search for first harmonic modulation in the right ascension distribution of cosmic rays detected at the Pierre Auger Observatory

Abstract

We present the results of searches for dipolar-type anisotropies in different energy ranges above 2.5 1017 eV with the surface detector array of the Pierre Auger Observatory, reporting on both the phase and the amplitude measurements of the first harmonic modulation in the right-ascension distribution. Upper limits on the amplitudes are obtained, which provide the most stringent bounds at present, being