Exploring arrival directions of UHECRs with the Yakutsk array

Abstract

The data on arrival directions of ultra-high energy cosmic rays (UHECRs) detected with the Yakutsk array are analyzed. The work is induced by the recent claim of the Pierre Auger collaboration for the significant correlation found between UHECRs and positions of nearby Active Galactic Nuclei (AGN) on the celestial sphere; and no correlation the HiRes collaboration stands for. Conflicting data of four giant arrays concern possible extragalactic sources of UHECRs and appeal to the profound analysis and to the future data from the Telescope Array/Northern Auger Observatory.

Testing for uniformity of ultra-high energy cosmic ray arrival directions

“…12 The mean value of the phase 33.2 0 ± 76.4 0 in the energy interval 10 < E < 31. 6 EeV is in agreement with other measurements 12,13 , while φ 1 ∼ 0 0 below 10 EeV is an artefact of the uniform distribution averaged in the interval φ 1 ∈ (−180 0 , 180 0 ).…”

“…Estimation of the diurnal and seasonal variations of the Yakutsk Array exposure have been given previously. 5,6 In this paper, however, estimations of the array exposure and corrections are not used. Instead, the RA distribution of CRs within the declination interval is tested for uniformity.…”

Zenith angle distribution of cosmic ray showers measured with the Yakutsk array and its application to the analysis of arrival directions in equatorial coordinates

“…At the highest energies where y > 1, the absorption of showers is negligible, S ef f is constant, and the distribution is compatible with the 'unabsorbed' f (θ) = 4 3 sin(2θ) [36,37]. It is formed by the dependence of the array acceptance on solid angle dΩ ∝ sin θ and on zenith angle ∝ cos θ.…”

Zenith angle distribution of cosmic ray showers measured with the Yakutsk array

“…2 on the right panel. At energies above 1 EeV, the absorption of showers is negligible, so the distribution is compatible with the 'isotropic' f (θ ) = 4 3 sin(2θ ) [33,34]. At lower energies, the particle density threshold cuts the right-hand tail of the distribution.…”