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

PIERRE AUGER COLLABORATION (J. ABRAHAM, ... , A. MARIAZZI, ET AL)

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS

IOP PUBLISHING LTD

Lugar: Londres; Año: 2012 vol. 4 p. 1 - 14

1475-7516

Observations of cosmic ray arrival directions made with the Pierre Auger Obser-vatory have previously provided evidence of anisotropy at the 99% CL using the correlationof ultra high energy cosmic rays (UHECRs) with objects drawn from the V´eron-Cetty V´eroncatalog. In this paper we report on the use of three catalog independent methods to searchfor 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 to study the impactsof sample size and magnetic smearing on their results, accounting for both angular and en-ergy resolutions. If the sources of UHECRs follow the same large scale structure as ordinarygalaxies in the local Universe and if UHECRs are deflected no more than a few degrees, astudy of mock maps suggests that these three methods can efficiently respond to the resultinganisotropy with a P-value = 1.0% or smaller with data sets as few as 100 events. Using datataken from January 1, 2004 to July 31, 2010 we examined the 20, 30, . . . , 110 highest energyevents with a corresponding minimum energy threshold of about 49.3EeV. The minimumP-values found were 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 multiple (correlated)scans performed on the data set, these catalog-independent methods do not yield strongevidence of anisotropy in the highest energy cosmic rays.