A search for anisotropy in the arrival directions of ultra high energy cosmic rays recorded at the Pierre Auger Observatory

THE PIERRE AUGER COLLABORATION.; S. J. SCIUTTO

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS

IOP PUBLISHING LTD

Lugar: Londres; Año: 2012

1475-7516

Observations of cosmic ray arrival directions made with the Pierre AugerObservatory have previously provided evidence of anisotropy at the 99% CLusing the correlation of ultra high energy cosmic rays (UHECRs) with ob-jects drawn from the V´eron-Cetty V´eron catalog. In this paper we reporton the use of three catalog independent methods to search for anisotropy.The 2pt–L, 2pt+ and 3pt methods, each giving a different measure of self-clustering in arrival directions, were tested on mock cosmic ray data sets tostudy the impacts of sample size and magnetic smearing on their results,accounting for both angular and energy resolutions. If the sources of UHE-CRs follow the same large scale structure as ordinary galaxies in the localUniverse and if UHECRs are deflected no more than a few degrees, a studyof mock maps suggests that these three methods can efficiently respond tothe resulting anisotropy with a P-value = 1.0% or smaller with data sets asfew as 100 events. Using data taken from January 1, 2004 to July 31, 2010 we examined the 20, 30, ..., 110 highest energy events with a correspondingminimum energy threshold of about 51 EeV. The minimum P-values foundwere 13.5% using the 2pt-L method, 1.0% using the 2pt+ method and 1.1%using the 3pt method for the highest 100 energy events. In view of the multi-ple (correlated) scans performed on the data set, these catalog-independentmethods do not yield strong evidence of anisotropy in the highest energycosmic rays.