Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory


P. Abreu, Argonne National Laboratory
M. Aglietta, Universidad Nacional Autónoma de México
E. J. Ahn, Universidad Nacional de La Plata
I. F.M. Albuquerque, Universidade Federal da Bahia
D. Allard, Bergische Universitat Wuppertal
I. Allekotte, Instituto Balseiro
J. Allen, Universidade de Sao Paulo - USP
P. Allison, Laboratoire de Physique Subatomique et de Cosmologie de Grenoble
J. Alvarez Castillo, University of Valencia
J. Alvarez-Mũniz, The Ohio State University
M. Ambrosio, INAF Istituto di Astrofisica Spaziale e Fisica Cosmica di Palermo
A. Aminaei, Universidad Complutense de Madrid
L. Anchordoqui, Colorado School of Mines
S. Andringa, Argonne National Laboratory
T. Antičić, Institut de Physique Nucléaire Orsay
A. Anzalone, Universidad Michoacana de San Nicolás de Hidalgo
C. Aramo, INAF Istituto di Astrofisica Spaziale e Fisica Cosmica di Palermo
E. Arganda, Michigan Technological University
F. Arqueros, Michigan Technological University
H. Asorey, Instituto Balseiro
P. Assis, Argonne National Laboratory
J. Aublin, Karlsruhe Institute of Technology, Campus North
M. Ave, Istituto Nazionale di Fisica Nucleare, Sezione di Genova
M. Avenier, Karlsruhe Institute of Technology, Campus South
G. Avila, Centro Brasileiro de Pesquisas Físicas
T. Bäcker, Università degli Studi di Napoli Federico II
M. Balzer, Universität Siegen
K. B. Barber, Pontificia Universidade Catolica do Rio de Janeiro
A. F. Barbosa, Universidade Estadual de Campinas
R. Bardenet, Karlsruhe Institute of Technology, Campus North
S. L.C. Barroso, Universidade Federal Fluminense
B. Baughman, Laboratoire de Physique Subatomique et de Cosmologie de Grenoble

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The Pierre Auger Collaboration has reported evidence for anisotropy in the distribution of arrival directions of the cosmic rays with energies E > Eth = 5.5 × 1019 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 > Eth are heavy nuclei with charge Z, the proton component of the sources shouldłead to excesses in the same regions at energies E/Z. We here report thełack of anisotropies in these directions at energies above Eth/Z (for illustrative values of Z = 6,13,26). If the anisotropies above Eth 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 thełower energies. © 2011 IOP Publishing Ltd and SISSA.

Publication Title

Journal of Cosmology and Astroparticle Physics