“Correlation of the highest-energy cosmic rays with the positions of nearby active galactic nuclei”

J. ABRAHAM (GARCIA, B. Y 400 AUTORES DE LA COL. INTERNACIONAL PIERRE AUGER)

ASTROPARTICLE PHYSICS

Elsevier

Lugar: Amsterdam; Año: 2008 vol. 29 p. 188 - 204

0927-6505

   Data collected by the Pierre Auger Observatory provide evidence for anisotropy in the arrival directions of the cosmic rays with thehighest-energies, which are correlated with the positions of relatively nearby active galactic nuclei (AGN) [Pierre Auger Collaboration,Science 318 (2007) 938]. The correlation has maximum significance for cosmic rays with energy greater than $6  1019 eV and AGN at adistance less than $75 Mpc. We have confirmed the anisotropy at a confidence level of more than 99% through a test with parametersspecified a priori, using an independent data set. The observed correlation is compatible with the hypothesis that cosmic rays with thehighest-energies originate from extra-galactic sources close enough so that their flux is not significantly attenuated by interaction with thecosmic background radiation (the Greisen–Zatsepin–Kuz’min effect). The angular scale of the correlation observed is a few degrees,which suggests a predominantly light composition unless the magnetic fields are very weak outside the thin disk of our galaxy. Our pres-ent data do not identify AGN as the sources of cosmic rays unambiguously, and other candidate sources which are distributed as nearbyAGN are not ruled out. We discuss the prospect of unequivocal identification of individual sources of the highest-energy cosmic rayswithin a few years of continued operation of the Pierre Auger Observatory.