2020/02/14 by The Pierre Auger Collaboration, A. Aab, P. Abreu +373 · 1 citation
Physics and Astronomy · #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/ab7236
published as Published in Astrophys. J 891 (2020)142 · Accepted by ApJ
arxiv created 2020/02/14 · arxiv updated 2021/01/11
We present measurements of the large-scale cosmic-ray anisotropies in right ascension, using data collected by the surface detector array of the Pierre Auger Observatory over more than 14 years. We determine the equatorial dipole component, d_⊥, through a Fourier analysis in right ascension that includes weights for each event so as to account for the main detector-induced systematic effects. For the energies at which the trigger efficiency of the array is small, the ``East-West'' method is employed. Besides using the data from the array with detectors separated by 1500 m, we also include data from the smaller but denser sub-array of detectors with 750 m separation, which allows us to extend the analysis down to ∼ 0.03 EeV. The most significant equatorial dipole amplitude obtained is that in the cumulative bin above 8~EeV, d_⊥=6.0+1.0-0.9%, which is inconsistent with isotropy at the 6σ level. In the bins below 8 EeV, we obtain 99% CL upper-bounds on d_⊥ at the level of 1 to 3 percent. At energies below 1 EeV, even though the amplitudes are not significant, the phases determined in most of the bins are not far from the right ascension of the Galactic center, at α\rm GC=-94^∘, suggesting a predominantly Galactic origin for anisotropies at these energies. The reconstructed dipole phases in the energy bins above 4 EeV point instead to right ascensions that are almost opposite to the Galactic center one, indicative of an extragalactic cosmic ray origin.