Cosmic-Ray Anisotropies in Right Ascension Measured by the Pierre Auger Observatory

THE PIERRE AUGER COLLABORATION.; S. J. SCIUTTO

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Londres; Año: 2020 vol. 891 p. 142 - 151

0004-637X

We present measurements of the large-scale cosmic-ray (CR) anisotropies in R.A., using data collected by thesurface detector array of the Pierre Auger Observatory over more than 14 yr. We determine the equatorial dipolecomponent, d^, through a Fourier analysis in R.A. that includes weights for each event so as to account for themain 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, wealso include data from the smaller but denser subarray of detectors with 750m separation, which allows us toextend the analysis down to ∼0.03EeV. The most significant equatorial dipole amplitude obtained is that in thecumulative bin above 8EeV, ^ = -d 6.0+0.91.0%, which is inconsistent with isotropy at the 6σ level. In the bins below8EeV, we obtain 99% CL upper bounds on d⊥ at the level of 1%?3%. At energies below 1EeV, even though theamplitudes are not significant, the phases determined in most of the bins are not far from the R.A. of the Galacticcenter, at αGC=−94°, suggesting a predominantly Galactic origin for anisotropies at these energies. Thereconstructed dipole phases in the energy bins above 4EeV point instead to R.A. that are almost opposite tothe Galactic center one, indicative of an extragalactic CR origin.