info:eu-repo/semantics/article
An Indication of Anisotropy in Arrival Directions of Ultra-high-energy Cosmic Rays through Comparison to the Flux Pattern of Extragalactic Gamma-Ray Sources
Date
2018-02Registration in:
Aab, A.; Allekotte, Ingomar; Almela, Daniel Alejandro; Andrada, B.; Bertou, Xavier Pierre Louis; et al.; An Indication of Anisotropy in Arrival Directions of Ultra-high-energy Cosmic Rays through Comparison to the Flux Pattern of Extragalactic Gamma-Ray Sources; IOP Publishing; Astrophysical Journal; 853; L29; 2-2018; 29-38
2041-8213
CONICET Digital
CONICET
Author
Aab, A.
Allekotte, Ingomar
Almela, Daniel Alejandro
Andrada, B.
Bertou, Xavier Pierre Louis
Botti, Ana Martina
Cancio, A.
Contreras, F.
Etchegoyen, Alberto
Figueira, Juan Manuel
Fuster, Alan Ezequiel
Golup, Geraldina Tamara
Gómez Berisso, M.
Gómez Vitale, P. F.
González, N.
Hampel, Matias Rolf
Hansen, Patricia Maria
Harari, Diego Dario
Holt, E.
Hulsman, Johannes
Josebachuili Ogando, Mariela Gisele
Kleinfeller, J.
Lucero, A.
Mollerach, Maria Silvia
Melo, Diego Gabriel
Müller, Ana Laura
Naranjo, I.
Roulet, Esteban
Rodriguez Rojo, J.
Sánchez, F.
Santos, E.
Sarmiento Cano, Christian Andres
Schmidt, D.
Sciutto, Sergio Juan
Silli, Gaia
Suarez, F.
Taborda Pulgarin, Oscar Alejandro
Wainberg, Oscar Isaac
Wundheiler, Brian
Yushkov, Alexey
The Pierre Auger Collaboration
Abstract
A new analysis of the data set from the Pierre Auger Observatory provides evidence for anisotropy in the arrivaldirections of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivalsfrom strong, nearby sources. The data consist of 5514 events above 20 EeV with zenith angles up to 80°recordedbefore 2017 April 30. Sky models have been created for two distinct populations of extragalactic gamma-rayemitters: active galactic nuclei from the second catalog of hard Fermi-LAT sources (2FHL) and starburst galaxiesfrom a sample that was examined with Fermi-LAT. Flux-limited samples, which include all types of galaxies fromthe Swift-BAT and 2MASS surveys, have been investigated for comparison. The sky model of cosmic-ray densityconstructed using each catalog has two free parameters, the fraction of events correlating with astrophysicalobjects, and an angular scale characterizing the clustering of cosmic rays around extragalactic sources. Amaximum-likelihood ratio test is used to evaluate the best values of these parameters and to quantify the strength ofeach model by contrast with isotropy. It is found that the starburst model fits the data better than the hypothesis ofisotropy with a statistical significance of 4.0σ, the highest value of the test statistic being for energies above39 EeV. The three alternative models are favored against isotropy with 2.7σ?3.2σ significance. The origin of theindicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed.