%0 Journal Article
%A Arganda, E.
%A Arqueros Martínez, Fernando
%A Blanco Ramos, Francisco
%A García Pinto, Diego
%A Ortiz Ramis, Montserrat
%A Rosado Vélez, Jaime
%A Vázquez Peñas, José Ramón
%T Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
%D 2011
%@ 1475-7516
%U https://hdl.handle.net/20.500.14352/45091
%X The Pierre Auger Collaboration has reported. evidence for anisotropy in the distribution of arrival directions of the cosmic rays with energies E > E-th = 5.5 x 10(19) eV. These show a correlation with the distribution of nearby extragalactic objects, including an apparent excess around the direction of Centaurus A. If the particles responsible for these excesses at E > E-th are heavy nuclei with charge Z, the proton component of the sources should lead to excesses in the same regions at energies E/Z. We here report the lack of anisotropies in these directions at energies above E-th/Z (for illustrative values of Z = 6, 13, 26). If the anisotropies above E-th are due to nuclei with charge Z, and under reasonable assumptions about the acceleration process, these observations imply stringent constraints on the allowed proton fraction at the lower energies.
%~