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

AAB, A.; ABREU, P.; AGLIETTA, M.; ALBUQUERQUE, I.F.M.; ALBURY, J.M.; ALLEKOTTE, I.; ALMELA, A.; CASTILLO, J. ALVAREZ; ALVAREZ-MUIZ, J.; ANASTASI, G.A.; ANCHORDOQUI, L.; ANDRADA, B.; ANDRINGA, S.; ARAMO, C.; FERREIRA, P. R. ARAÚJO; ASOREY, H.; ASSIS, P.; AVILA, G.; BADESCU, A.M.; BAKALOVA, A.; BALACEANU, A.; BARBATO, F.; LUZ, R. J. BARREIRA; BECKER, K.H.; BELLIDO, J.A.; BERAT, C.; BERTAINA, M.E.; BERTOU, X.; BIERMANN, P.L.; BISTER, T.; BITEAU, J.; BLANCO, A.; BLAZEK, J.; BLEVE, C.; BOHÁ?OVÁ, M.; BONCIOLI, D.; BONIFAZI, C.; ARBELETCHE, L. BONNEAU; BORODAI, N.; BOTTI, A.M.; BRACK, J.; BRETZ, T.; BRIECHLE, F.L.; BUCHHOLZ, P.; BUENO, A.; BUITINK, S.; BUSCEMI, M.; CABALLERO-MORA, K.S.; CACCIANIGA, L.; CALCAGNI, L.; CANCIO, A.; CANFORA, F.; CARACAS, I.; CARCELLER, J.M.; CARUSO, R.; CASTELLINA, A.; CATALANI, F.; CATALDI, G.; CAZON, L.; CERDA, M.; CHINELLATO, J.A.; CHOI, K.; CHUDOBA, J.; CHYTKA, L.; CLAY, R.W.; CERUTTI, A. C. COBOS; COLALILLO, R.; COLEMAN, A.; COLUCCIA, M.R.; CONCEICA¸Õ, R.; CONDORELLI, A.; CONS

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Año: 2020 vol. 891

0004-637X

We present measurements of the large-scale cosmic-ray (CR) anisotropies in R.A., using data collected by the surface detector array of the Pierre Auger Observatory over more than 14 yr. We determine the equatorial dipole component, through a Fourier analysis in R.A. 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 subarray 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, %, 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%-3%. 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 R.A. of the Galactic center, at 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 R.A. that are almost opposite to the Galactic center one, indicative of an extragalactic CR origin.