Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter

ABREU, P.; AGLIETA, M; AHN, E; GARCIA, B (400 AUTORES ORDEN ALFABETICO)

ASTROPARTICLE PHYSICS

ELSEVIER SCIENCE BV

Año: 2010 vol. 34 p. 314 - 326

0927-6505

Data collected by the Pierre Auger Observatory through 31 August 2007 showed evidence for anisotropyin the arrival directions of cosmic rays above the Greisen–Zatsepin–Kuz’min energy threshold, 6  1019 eV. The anisotropy was measured by the fraction of arrival directions that are less than 3.1° fromthe position of an active galactic nucleus within 75 Mpc (using the Véron-Cetty and Véron 12th catalog).An updated measurement of this fraction is reported here using the arrival directions of cosmic rays recorded above the same energy threshold through 31 December 2009. The number of arrival directionshas increased from 27 to 69, allowing a more precise measurement. The correlating fraction is 38þ7 %,À6 compared with 21% expected for isotropic cosmic rays. This is down from the early estimate of 69þ11 %.À13The enlarged set of arrival directions is examined also in relation to other populations of nearby extraga-lactic objects: galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in hard X-raysby the Swift Burst Alert Telescope. A celestial region around the position of the radiogalaxy Cen A has thelargest excess of arrival directions relative to isotropic expectations. The 2-point autocorrelation functionis shown for the enlarged set of arrival directions and compared to the isotropic expectation.