Measurement of the first harmonic modulation in the right ascension distribution of cosmic rays detected at the Pierre Auger Observatory: towards the detection of dipolar anisotropies over a wide energy range

Abstract

First harmonic analyses of the right ascension distribution of cosmic rays detected at the Pierre AugerObservatory are reported. We here update the upper limits on the dipole component in the equatorial plane andextend the previous results to lower energies by using data recorded by the infill surface detector array. On theother hand, a possible consistency in ordered energy intervals of the phase was observed and reported, consistencythat may be indicative of anisotropies whose amplitudes are too small to stand out above the background noiseinduced by the finite statistics accumulated so far. Based on this posterior observation, a prescribed single shot testwas designed on June 25 2011 to establish at 99% CL whether this consistency is real or not. Since the effecthas been observed over a wide energy range, the test makes use of data of both the infill and the regular surfacedetector arrays. At about mid-term, the status of this prescription is reported.