UHECR arrival directions in the latest data from the original Auger and TA surface detectors and nearby galaxies
Armando di Matteo, Luis A. Anchordoqui, Teresa Bister, Jonathan Biteau, Lorenzo Caccianiga, Rogerio M. de Almeida, Olivier Deligny, Ugo GIACCARI, Diego Harari, Jihyun Kim, M. Kuznetsov, Ioana Codrina Maris, Г. И. Рубцов, Petr Tinyakov, S. Troitsky, F. Urban, P. Abreu, M. Aglietta, Justin M. Albury, I. Allekotte, Alejandro Almela, Jaime Álvarez-Muñiz, Rafael Alves Batista, Gioacchino Alex Anastasi, Belén Andrada, S. Andringa, C. Aramo, Paulo Ricardo Araújo Ferreira, Juan Carlos Arteaga Velázquez, Hernán Gonzalo Asorey, P. Assis, Gualberto Avila, Alina Mihaela Badescu, Alena Bakalová, Alexandru Balaceanu, Felicia Barbato, Ricardo Jorge Barreira Luz, Karl‐Heinz Becker, Jose A. Bellido, Corinne Bérat, Mario E. Bertaina, X. Bertou, Peter L. Biermann, Virginia Binet, Kathrin Bismark, Jiří Blažek, C. Bleve, Martina Boháčová, Denise Boncioli, C. Bonifazi, Luan Bonneau Arbeletche, Nataliia Borodai, Ana Martina Botti, Jeffrey Brack, T. Bretz, P. Gabriel Brichetto Orchera, Florian Lukas Briechle, P. Buchholz, A. Bueno, S. Buitink, Mario Buscemi, Max Büsken, K. S. Caballero‐Mora, Fabrizia Canfora, Ioana Caracas, Juan Miguel Carceller, R. Caruso, A. Castellina, Fernando Catalani, G. Cataldi, Lorenzo Cazon, Marcos Cerda, J. A. Chinellato, J. Chudoba, L. Chytka, R. W. Clay, Agustín Cobos Cerutti, Roberta Colalillo, Alan Coleman, Maria Rita Coluccia, R. Conceição, Antonio Condorelli, Giovanni Consolati, F. Contreras, Fabio Convenga, Diego Correia dos Santos, C. E. Covault, S. Dasso, K. Daumiller, B. R. Dawson, Jarryd A. Day, Joaquin de Jesus, S. J. de Jong, G. De Mauro, João de Mello Neto, I. De Mitri, Jaime de Oliveira, Danelise de Oliveira Franco, Francesco de Palma, Vitor de Souza
Abstract
The distribution of ultra-high-energy cosmic-ray arrival directions appears to be nearly isotropic except for a dipole moment of order $6 \times (E/10~\mathrm{EeV})$ per cent. Nonetheless, at the highest energies, as the number of possible candidate sources within the propagation horizon and the magnetic deflections both shrink, smaller-scale anisotropies might be expected to emerge. On the other hand, the flux suppression reduces the statistics available for searching for such anisotropies. In this work, we consider two different lists of candidate sources: a sample of nearby starburst galaxies and the 2MRS catalog tracing stellar mass within $250~\mathrm{Mpc}$. We combine surface-detector data collected at the Pierre Auger Observatory until 2020 and the Telescope Array until 2019, and use them to test models in which UHECRs comprise an isotropic background and a foreground originating from the candidate sources and randomly deflected by magnetic fields. The free parameters of these models are the energy threshold, the signal fraction, and the search angular scale. We find a correlation between the arrival directions of $11.8\%_{-3.1\%}^{+5.0\%}$ of cosmic rays detected with $E \ge 38~\mathrm{EeV}$ by Auger or with $E \gtrsim 49~\mathrm{EeV}$ by TA and the position of nearby starburst galaxies on a ${15.5^\circ}_{-3.2^\circ}^{+5.3^\circ}$ angular scale, with a $4.2\sigma$ post-trial significance, as well as a weaker correlation with the overall galaxy distribution.