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

THE PIERRE AUGER COLLABORATION; GARCIA, B (COMO PARTE DE THE PIERRE AUGER COLLABORATION)

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Londres; Año: 2020 vol. 891 p. 142 - 155

0004-637X

Wepresent measurements of the large-scale cosmic-ray (CR) anisotropiesin R.A., using data collected by the surface detector array of thePierre Auger Observatory over more than 14 yr. We determine theequatorial dipole component, ,through a Fourier analysis in R.A. that includes weights for eachevent so as to account for the main detector-induced systematiceffects. For the energies at which the trigger efficiency of thearray is small, the "east?west" method is employed.Besides using the data from the array with detectors separated by1500 m, we also include data from the smaller but densersubarray of detectors with 750 m separation, which allows us toextend the analysis down to ~0.03 EeV. The most significantequatorial dipole amplitude obtained is that in the cumulative binabove 8 EeV, %,which is inconsistent with isotropy at the 6σlevel. In the bins below 8 EeV, we obtain 99% CL upper bounds ond⊥at the level of 1%?3%. At energies below 1 EeV, even thoughthe amplitudes are not significant, the phases determined in most ofthe bins are not far from the R.A. of the Galactic center, at αGC = −94°,suggesting a predominantly Galactic origin for anisotropies at theseenergies. The reconstructed dipole phases in the energy bins above4 EeV point instead to R.A. that are almost opposite to theGalactic center one, indicative of an extragalactic CR origin.p { margin-bottom: 0.1in; line-height: 115%; background: transparent }