Search for Anisotropy in the Ultra High Energy Cosmic Ray Spectrum using\n the Telescope Array Surface Detector

Le résumé fourni par la source

The Telescope Array (TA) experiment is located in the western desert of Utah,\nUSA, and observes ultra high energy cosmic rays (UHECRs) in the Northern\nhemisphere. At the highest energies, $E>10$~EeV, the shape of cosmic ray energy\nspectrum may carry an imprint of the source density distribution along the line\nof sight different in different directions of the sky. In this study, we search\nfor such directional variations in the shape of the energy spectrum using\nevents observed with the Telescope Array's surface detector. We divide the TA\nfield of view into two nearly equal-exposure regions: the "on-source" region\nwhich we define as $\\pm 30^\\circ$ of the supergalactic plane containing mostly\nnearby structures, and the complementary "off-source" region where the sources\nare further away on average. We compare the UHECR spectra in these regions by\nfitting them to the broken power law and comparing the resulting parameters. We\nfind that the off-source spectrum has an earlier break at highest energies. The\nchance probability to obtain such or larger difference in statistically\nequivalent distributions is estimated as $6.2\\pm1.1\\times10^{-4}$ ($3.2\\sigma$)\nby a Monte-Carlo simulation. The observed difference in spectra is in a\nreasonable quantitative agreement with a simplified model that assumes that the\nUHECR sources trace the galaxy distribution from the 2MRS catalogue, primary\nparticles are protons and the magnetic deflections can be neglected.\n

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.