The effect of the geomagnetic field on cosmic ray energy estimates and large scale anisotropy searches on data from the Pierre Auger Observatory

Abstract

We present a comprehensive study of the influence of the geomagnetic field on\nthe energy estimation of extensive air showers with a zenith angle smaller than\n$60^\\circ$, detected at the Pierre Auger Observatory. The geomagnetic field\ninduces an azimuthal modulation of the estimated energy of cosmic rays up to\nthe ~2% level at large zenith angles. We present a method to account for this\nmodulation of the reconstructed energy. We analyse the effect of the modulation\non large scale anisotropy searches in the arrival direction distributions of\ncosmic rays. At a given energy, the geomagnetic effect is shown to induce a\npseudo-dipolar pattern at the percent level in the declination distribution\nthat needs to be accounted for.\n