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

TL;DR

This study analyzes the zenith angle distribution of ultra-high energy cosmic ray showers measured by the Yakutsk array and applies it to examine their arrival directions in equatorial coordinates, providing insights into cosmic ray origins.

Contribution

It revisits Yakutsk array data to interpret zenith angle distributions and their relation to shower parameters, extending analysis to lower energies and mapping arrival directions.

Findings

Distribution consistent with expectations, no anisotropy detected.

Upper limits set on cosmic ray source contributions.

Analysis extends to energies below 10^{18} eV.

Abstract

The Yakutsk array dataset in the energy interval $(10^{17},10^{19})$ eV is revisited in order to interpret the zenith angle distribution of an extensive air shower event rate of ultra-high energy cosmic rays. The close relation of the distribution to the attenuation of the main measurable parameter of showers, $S_{600}$, is examined. Measured and expected distributions are used to analyze the arrival directions of cosmic rays on an equatorial map including the energy range below $10^{18}$ eV, which was previously avoided due to the reduced trigger efficiency of the array in the range. While the null hypothesis cannot be rejected with data from the Yakutsk array, an upper limit on the fraction of cosmic rays from a separable source in the uniform background is derived as a function of declination and energy.