Large-scale anisotropies above 0.03 EeV measured by the Pierre Auger Observatory

ESTEBAN ROULET, FOR THE PIERRE AUGER COLLABORATION

Congreso; 36th International Cosmic Ray Conference (ICRC 2019); 2019

We present analyses of the large-scale anisotropies observed by the Pierre Auger Observatory overmore than three decades in energy, considering data since 1 January 2004 up to 31 August 2018.ForE≥4 EeV, for which the array with 1500 m separation between detectors is fully efficient,we obtain the dipolar and quadrupolar amplitudes through a combined Fourier analysis of thedistribution of events in right ascension and azimuth. A dipolar modulation with an amplituded=6.6+1.2−0.8% and pointing∼125◦away from the Galactic center is observed above 8 EeV. Thedipole amplitude shows an indication of an increase with energy above 4 EeV and the quadrupolarcomponents turn out to be not significant. Astrophysical scenarios that could account for theseresults are briefly discussed. We also extend the study of the equatorial component of the dipolarmodulation down to∼0.03 EeV. In the regime in which the efficiencies are small, we use the East-West method, which is largely insensitive to systematic effects. Finally, for the lowest energieswe use the data from a subarray with 750 m separation between detectors. The results suggest achange in the phase of the equatorial dipole from values pointing close to the right ascension ofthe Galactic center below EeV energies towards values indicative of an extragalactic origin forthe dipolar anisotropy above a few EeV.