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

TL;DR

This paper investigates how Earth's magnetic field affects cosmic ray energy measurements and anisotropy searches at the Pierre Auger Observatory, revealing azimuthal modulations and proposing correction methods.

Contribution

It provides a detailed analysis of geomagnetic effects on energy estimation and introduces a correction method to improve anisotropy studies.

Findings

Geomagnetic field causes up to 2% azimuthal modulation in energy estimates.

A pseudo-dipolar pattern at the percent level is induced in declination distributions.

The proposed correction method mitigates geomagnetic effects in anisotropy analyses.

Abstract

We present a comprehensive study of the influence of the geomagnetic field on the energy estimation of extensive air showers with a zenith angle smaller than $60^\circ$, detected at the Pierre Auger Observatory. The geomagnetic field induces an azimuthal modulation of the estimated energy of cosmic rays up to the ~2% level at large zenith angles. We present a method to account for this modulation of the reconstructed energy. We analyse the effect of the modulation on large scale anisotropy searches in the arrival direction distributions of cosmic rays. 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.