An Indication of Anisotropy in Arrival Directions of Ultra-high-energy Cosmic Rays through Comparison to the Flux Pattern of Extragalactic Gamma-Ray Sources<sup>*</sup>
A. AabIMAPP, Radboud University Nijmegen, Nijmegen, The NetherlandsP. AbreuLIP - Laboratory of Instrumentation and Experimental Particle PhysicsM. AgliettaINFN, Sezione di Torino, Torino, ItalyI. F. M. AlbuquerqueUniversidade de São Paulo, Instituto de Física, São Paulo, SP, BrazilI. AllekotteBalseiro InstituteA. AlmelaInstituto de Tecnologías en Detección y AstropartículasJ. Alvarez CastilloUniversidad Nacional Autónoma de México, México, D.F., MéxicoJaime Álvarez-MuñizUniversidad de Santiago de Compostela, Santiago de Compostela, SpainGioacchino Alex AnastasiGran Sasso Science Institute (INFN), L'Aquila, ItalyLuis A. AnchordoquiCity University of New YorkBelén AndradaInstituto de Tecnologías en Detección y Astropartículas (CNEA, CONICET, UNSAM), Buenos Aires, ArgentinaS. AndringaLIP - Laboratory of Instrumentation and Experimental Particle PhysicsC. AramoINFN, Sezione di Napoli, Napoli, ItalyN. ArseneInstitute of Space Science, Bucharest-Magurele, RomaniaH. AsoreyBalseiro InstituteP. AssisLaboratório de Instrumentação e Física Experimental de Partículas—LIP and Instituto Superior Técnico—IST, Universidade de Lisboa—UL, Lisboa, PortugalG. ÁvilaObservatorio Pierre Auger, Malargüe, ArgentinaAlina Mihaela BadescuUniversity Politehnica of Bucharest, Bucharest, RomaniaA. Balaceanu"Horia Hulubei" National Institute for Physics and Nuclear Engineering, Bucharest-Magurele, RomaniaFelicia BarbatoUniversità di Napoli "Federico II," Dipartimento di Fisica "Ettore Pancini," Napoli, ItalyRicardo Jorge Barreira LuzLaboratório de Instrumentação e Física Experimental de Partículas—LIP and Instituto Superior Técnico—IST, Universidade de Lisboa—UL, Lisboa, PortugalJ. J. BeattyOhio State University, Columbus, OH, USAK. BeckerBergische Universität Wuppertal, Department of Physics, Wuppertal, GermanyJose A. BellidoUniversity of Adelaide, Adelaide, S.A., AustraliaCorinne BératUniversité Grenoble AlpesM. E. BertainaUniversità Torino, Dipartimento di Fisica, Torino, ItalyX. BertouCentro Atómico Bariloche and Instituto Balseiro (CNEA-UNCuyo-CONICET), San Carlos de Bariloche, ArgentinaPeter L. BiermannMax-Planck-Institut für Radioastronomie, Bonn, GermanyJonathan BiteauInstitut National de Physique Nucléaire et de Physique des ParticulesS. G. BlaessUniversity of Adelaide, Adelaide, S.A., AustraliaA. BlancoLIP - Laboratory of Instrumentation and Experimental Particle PhysicsJiří BlažekInstitute of Physics of the Czech Academy of Sciences, Prague, Czech RepublicC. BleveINFN, Sezione di Lecce, Lecce, ItalyM. BoháčováInstitute of Physics of the Czech Academy of Sciences, Prague, Czech RepublicC. BonifaziUniversidade Federal do Rio de Janeiro, Instituto de Física, Rio de Janeiro, RJ, BrazilNataliia BorodaiInstitute of Nuclear Physics PAN, Krakow, PolandAna Martina BottiKarlsruhe Institute of Technology, Institut für Kernphysik, Karlsruhe, GermanyJ. BrackColorado State University, Fort Collins, CO, USAI.M. Brâncuş"Horia Hulubei" National Institute for Physics and Nuclear Engineering, Bucharest-Magurele, RomaniaT. BretzRWTH Aachen University, III. Physikalisches Institut A, Aachen, GermanyA. BridgemanKarlsruhe Institute of Technology, Institut für Experimentelle Kernphysik (IEKP), Karlsruhe, GermanyF. L. BriechleRWTH Aachen University, III. Physikalisches Institut A, Aachen, GermanyP. BuchholzUniversität Siegen, Fachbereich 7 Physik—Experimentelle Teilchenphysik, Siegen, GermanyA. BuenoUniversidad de Granada and C.A.F.P.E., Granada, SpainS. BuitinkIMAPP, Radboud University Nijmegen, Nijmegen, The NetherlandsMario BuscemiINFN, Sezione di Catania, Catania, ItalyK. S. Caballero‐MoraUniversidad Autónoma de Chiapas, Tuxtla Gutiérrez, Chiapas, MéxicoLorenzo CaccianigaUniversità di Milano, Dipartimento di Fisica, Milano, ItalyA. CancioUniversidad Tecnológica Nacional—Facultad Regional Buenos Aires, Buenos Aires, ArgentinaF. CanforaIMAPP, Radboud University Nijmegen, Nijmegen, The NetherlandsR. CarusoUniversità di Catania, Dipartimento di Fisica e Astronomia, Catania, ItalyA. CastellinaOsservatorio Astrofisico di Torino (INAF), Torino, ItalyF. CatalaniUniversidade de São Paulo, Escola de Engenharia de Lorena, Lorena, SP, BrazilG. CataldiINFN, Sezione di Lecce, Lecce, ItalyLorenzo CazonLaboratório de Instrumentação e Física Experimental de Partículas—LIP and Instituto Superior Técnico—IST, Universidade de Lisboa—UL, Lisboa, PortugalA. G. ChavezUniversidad Michoacana de San Nicolás de Hidalgo, Morelia, Michoacán, MéxicoC. DobrigkeitUniversidade Estadual de Campinas, IFGW, Campinas, SP, BrazilJ. ChudobaInstitute of Physics of the Czech Academy of Sciences, Prague, Czech RepublicR. W. ClayUniversity of Adelaide, Adelaide, S.A., AustraliaAgustín Cobos CeruttiNational University of General San MartínRoberta ColalilloINFN, Sezione di Napoli, Napoli, ItalyAlan ColemanPennsylvania State University, University Park, PA, USAL. CollicaINFN, Sezione di Torino, Torino, ItalyM. R. ColucciaUniversità del Salento, Dipartimento di Matematica e Fisica "E. De Giorgi," Lecce, ItalyR. ConceiçãoLIP - Laboratory of Instrumentation and Experimental Particle PhysicsGiovanni ConsolatiINFN, Sezione di Milano, Milano, ItalyF. ContrerasObservatorio Pierre Auger, Malargüe, ArgentinaM. J. CooperUniversity of Adelaide, Adelaide, S.A., AustraliaS. CoutuPennsylvania State University, University Park, PA, USAC. E. CovaultCase Western Reserve University, Cleveland, OH, USAJ. CroninUniversity of ChicagoS. D’AmicoINFN, Sezione di Lecce, Lecce, ItalyB. DanielUniversidade Estadual de Campinas, IFGW, Campinas, SP, BrazilS. DassoInstituto de Astronomía y Física del Espacio (IAFE, CONICET-UBA), Buenos Aires, ArgentinaK. DaumillerKarlsruhe Institute of Technology, Institut für Kernphysik, Karlsruhe, GermanyB. R. DawsonUniversity of Adelaide, Adelaide, S.A., AustraliaR. M. de AlmeidaUniversidade Federal Fluminense, EEIMVR, Volta Redonda, RJ, BrazilS. J. de JongNationaal Instituut voor Kernfysica en Hoge Energie Fysica (NIKHEF), Science Park, Amsterdam, The NetherlandsG. De MauroIMAPP, Radboud University Nijmegen, Nijmegen, The NetherlandsJ. R. T. de Mello NetoUniversidade Federal do Rio de Janeiro, Instituto de Física, Rio de Janeiro, RJ, BrazilI. De MitriINFN, Sezione di Lecce, Lecce, ItalyJaime de OliveiraUniversidade Federal Fluminense, EEIMVR, Volta Redonda, RJ, BrazilV. de SouzaUniversidade de São Paulo, Instituto de Física de São Carlos, São Carlos, SP, BrazilJ. DebatinKarlsruhe Institute of Technology, Institut für Experimentelle Kernphysik (IEKP), Karlsruhe, GermanyO. DelignyInstitut National de Physique Nucléaire et de Physique des ParticulesM. L. Díaz CastroUniversidade Estadual de Campinas, IFGW, Campinas, SP, BrazilF. DiogoLIP - Laboratory of Instrumentation and Experimental Particle PhysicsC. DobrigkeitUniversidade Estadual de Campinas, IFGW, Campinas, SP, BrazilJ. C. D’OlivoUniversidad Nacional Autónoma de México, México, D.F., MéxicoQ. DorostiUniversität Siegen, Fachbereich 7 Physik—Experimentelle Teilchenphysik, Siegen, GermanyR. C. dos AnjosUniversidade Federal do Paraná, Setor Palotina, Palotina, BrazilM. T. DovaUniversidad Nacional de La PlataA. DundovicUniversität Hamburg, II. Institut für Theoretische Physik, Hamburg, GermanyJan EbrInstitute of Physics of the Czech Academy of Sciences, Prague, Czech RepublicR. EngelKarlsruhe Institute of Technology, Institut für Kernphysik, Karlsruhe, GermanyM. ErdmannRWTH Aachen University, III. Physikalisches Institut A, Aachen, GermanyMostafa ErfaniFolkwang University of the ArtsC. O. EscobarFermi National Accelerator Laboratory, Batavia, IL, USAJ. EspadanalLIP - Laboratory of Instrumentation and Experimental Particle PhysicsA. EtchegoyenInstituto de Tecnologías en Detección y Astropartículas
2018en
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Abstract A new analysis of the data set from the Pierre Auger Observatory provides evidence for anisotropy in the arrival directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals from strong, nearby sources. The data consist of 5514 events above with zenith angles up to 80° recorded before 2017 April 30. Sky models have been created for two distinct populations of extragalactic gamma-ray emitters: active galactic nuclei from the second catalog of hard Fermi -LAT sources (2FHL) and starburst galaxies from a sample that was examined with Fermi -LAT. Flux-limited samples, which include all types of galaxies from the Swift -BAT and 2MASS surveys, have been investigated for comparison. The sky model of cosmic-ray density constructed using each catalog has two free parameters, the fraction of events correlating with astrophysical objects, and an angular scale characterizing the clustering of cosmic rays around extragalactic sources. A maximum-likelihood ratio test is used to evaluate the best values of these parameters and to quantify the strength of each model by contrast with isotropy. It is found that the starburst model fits the data better than the hypothesis of isotropy with a statistical significance of 4.0 σ , the highest value of the test statistic being for energies above . The three alternative models are favored against isotropy with 2.7 σ –3.2 σ significance. The origin of the indicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed.
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