Influence of geomagnetic effects on large scale anisotropy searches

THE PIERRE AUGER COLLABORATION (AUTOR 434 DE 474); M. TUEROS (COAUTOR)

Beijing

Conferencia; 32nd International Cosmic Ray Conference 2011; 2011

Institute of High Energy Physics, Chinese Academy of Sciences

We discuss the influence of the geomagnetic field on the energy estimate of extensive air showers with zenith angles smaller than 60◦, detected with the Surface Detector array of the Pierre Auger Observatory. The geomagnetic field induces a modulation of the energy estimator, depending on the shower direction, at the ∼ 2% level at large zenith angles. We present a method to account for this modulation in the reconstruction of the energy of the cosmic rays. We analyse the effect of the energy shift on large scale anisotropy searches in the arrival direction distributions of cosmic rays above the energy threshold at which the detection efficiency of the surface detector array is saturated (3 EeV). At a given energy, the geomagnetic effect is shown to induce a pseudo-dipolar pattern at the percent level in the declination distribution that needs to be accounted for before performing large scale anisotropy searches.