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


A. Aab, Radboud University Nijmegen
P. Abreu, Instituto Superior Técnico
M. Aglietta, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
I. F.M. Albuquerque, Universidade de Sao Paulo - USP
J. M. Albury, The University of Adelaide
I. Allekotte, Centro Atomico Bariloche
A. Almela, Universidad Nacional de San Martin
J. Alvarez Castillo, Universidad Nacional Autónoma de México
J. Alvarez-Muiz, Universidad de Santiago de Compostela
G. A. Anastasi, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
L. Anchordoqui, Lehman College
B. Andrada, Universidad Nacional de San Martin
S. Andringa, Instituto Superior Técnico
C. Aramo, Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
P. R.Araújo Ferreira, Rheinisch-Westfälische Technische Hochschule Aachen
H. Asorey, Universidad Nacional de San Martin
P. Assis, Instituto Superior Técnico
G. Avila, Pierre Auger Observatory
A. M. Badescu, University Politehnica of Bucharest
A. Bakalova, Institute of Physics of the Czech Academy of Sciences
A. Balaceanu, Horia Hulubei National Institute of Physics and Nuclear Engineering
F. Barbato, Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
R. J.Barreira Luz, Instituto Superior Técnico
K. H. Becker, Bergische Universitat Wuppertal
J. A. Bellido, The University of Adelaide
C. Berat, Universite Grenoble Alpes
M. E. Bertaina, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
X. Bertou, Centro Atomico Bariloche
P. L. Biermann, Max Planck Institute for Radio Astronomy
T. Bister, Rheinisch-Westfälische Technische Hochschule Aachen
J. Biteau, Institut de Physique Nucléaire Orsay
A. Blanco, Instituto Superior Técnico
B. Fick, Michigan Technological UniversityFollow
D. F. Nitz, Michigan Technological UniversityFollow
A. Puyleart, Michigan Technological University

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Department of Physics


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.

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Publication Title

Astrophysical Journal