Cosmic-Ray Anisotropies in Right Ascension Measured by the Pierre Auger Observatory
A. Aab, P. Abreu, M. Aglietta, I. F. M. Albuquerque, Justin M. Albury, I. Allekotte, A. Almela, M. Castillo, Jaime Álvarez-Muñiz, Gioacchino Alex Anastasi, Luis A. Anchordoqui, B. Andrada, S. Andringa, C. Aramo, P. R. Araújo Ferreira, Hernán Gonzalo Asorey, P. Assis, Gael Flores Avila, Alina Mihaela Badescu, Alena Bakalová, A. Balaceanu, Felicia Barbato, Ricardo Jorge Barreira Luz, K. H. Becker, Jose A. Bellido, C. Bérat, M. E. Bertaina, X. Bertou, Peter L. Biermann, Teresa Bister, Jonathan Biteau, A. Blanco, J. Blazek, C. Bleve, M. Boháčová, Denise Boncioli, C. Bonifazi, L. Bonneau Arbeletche, Nataliia Borodai, Ana Martina Botti, J. Brack, T. Bretz, F. L. Briechle, P. Buchholz, A. Bueno, S. Buitink, Mario Buscemi, K. S. Caballero‐Mora, Lorenzo Caccianiga, L. Calcagni, A. Cancio, F. Canfora, Ioana Caracas, J. M. Carceller, R. Caruso, A. Castellina, F. Catalani, G. Cataldi, Lorenzo Cazon, M. Cerda, J. A. Chinellato, K. Choi, J. Chudoba, L. Chytka, R. W. Clay, A. C. Cobos Cerutti, R. Colalillo, A. Coleman, M. R. Coluccia, R. Conceição, Antonio Condorelli, Giovanni Consolati, F. Contreras, Fabio Convenga, C. E. Covault, S. Dasso, K. Daumiller, B. R. Dawson, J.A. Day, R. M. de Almeida, Joaquín de Jesús, S. J. de Jong, G. De Mauro, J. R. T. de Mello Neto, I. De Mitri, J. de Oliveira, Danelise de Oliveira Franco, V. de Souza, J. Debatin, Mariano del Río, O. Deligny, N. Dhital, Armando di Matteo, M. L. Díaz Castro, C. Dobrigkeit, J. C. D’Olivo, Q. Dorosti, R. C. dos Anjos, M. T. Dova, Jan Ebr
Abstract
Abstract 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 6 σ 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 α 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.