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Ivanov A.A.,Shafer Institute for Cosmophysical Research and Aeronomy
Astrophysical Journal

This paper presents the results of searches for anisotropy in the arrival directions of ultra-high-energy cosmic rays (CRs) detected with the Yakutsk Array during the 1974-2008 observational period as well as searches in available data from other giant extensive air shower arrays working at present. A method of analysis based on a comparison of the minimum width of distributions in equatorial coordinates is used. As a result, a hypothesis of isotropy in arrival directions is rejected at the 99.5% significance level. The observed decrease in the minimum width of the distribution can be explained by the presence of CR sources in energy intervals and sky regions according to recent indications inferred from data of the Yakutsk Array and Telescope Array experiments. © 2015. The American Astronomical Society. All rights reserved. Source

Ivanov A.A.,Shafer Institute for Cosmophysical Research and Aeronomy
Astrophysical Journal

The energy spectra of ultrahigh energy cosmic rays (CRs) measured with giant extensive air shower (EAS) arrays exhibit discrepancies between the flux intensities and/or estimated CR energies exceeding experimental errors. The well-known intensity correction factor due to the dispersion of the measured quantity in the presence of a rapidly falling energy spectrum is insufficient to explain the divergence. Another source of systematic energy determination error is proposed concerning the charged particle density measured with the surface arrays, which arises due to simplifications (namely, the superposition approximation) in nucleus-nucleus interaction description applied to the shower modeling. Making use of the essential correction factors results in congruous CR energy spectra within experimental errors. Residual differences in the energy scales of giant arrays can be attributed to the actual overall accuracy of the EAS detection technique used. CR acceleration and propagation model simulations using the dip and ankle scenarios of the transition from galactic to extragalactic CR components are in agreement with the combined energy spectrum observed with EAS arrays. © 2010. The American Astronomical Society. Source

One of the main goals of investigations using present and future giant extensive air shower (EAS) arrays is the mass composition of ultra-high energy cosmic rays (UHECRs). A new approach to the problem is presented, combining the analysis of arrival directions with the statistical test of the paired EAS samples. One of the ideas of the method is to search for possible correlations between UHECR masses and their separate sources; for instance, if there are two sources in different areas of the celestial sphere injecting different nuclei, but the fluxes are comparable so that arrival directions are isotropic, then the aim is to reveal a difference in the mass composition of cosmic-ray fluxes. The method is based on a non-parametric statistical test - the Wilcoxon signed-rank routine - which does not depend on the populations fitting any parameterized distributions. Two particular algorithms are proposed: first, using measurements of the depth of the EAS maximum position in the atmosphere; and second, relying on the age variance of air showers initiated by different primary particles. The formulated method is applied to the Yakutsk array data, in order to demonstrate the possibility of searching for a difference in average mass composition between the two UHECR sets, arriving particularly from the supergalactic plane and a complementary region. © 2013. The American Astronomical Society. All rights reserved.. Source

Ivanov A.A.,Shafer Institute for Cosmophysical Research and Aeronomy
International Journal of Modern Physics D

Arrival directions of ultra-high energy cosmic rays (UHECRs) exhibit mainly an isotropic distribution with some small deviations in particular energy bins. In this paper, the Yakutsk array data are tested for circular uniformity of arrival directions in right ascension (RA) using two methods appropriate for the energy ranges below and above (Formula presented.) eV. No statistically significant deviation from uniformity is found in the arrival directions of cosmic rays (CRs) detected within the observation period 1974–2000. © 2016 World Scientific Publishing Company Source

Anatoly I.,Shafer Institute for Cosmophysical Research and Aeronomy
EPJ Web of Conferences

The results of the Yakutsk array experiment aimed at investigations of ultra-high energy cosmic rays (UHECRs) are presented. We outline the current status of the instrument and an outlook for future directions and areas of study. © Owned by the authors, published by EDP Sciences, 2013. Source

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