ARGO-YBJ Observation of the Large-scale Anisotropy During the Solar Minimum between Cycles 23 and 24

Abstract

This paper reports on the measurement of the large-scale anisotropy in the distribution of cosmic-ray arrival directions using the data collected by the air shower detector ARGO-YBJ from 2008 January to 2009 December,during the minimum of solar activity between cycles 23 and 24. In this period, more than 200 billion showers were recorded with energies between 1 and 30 TeV. The observed two-dimensional distribution of cosmic rays is characterized by two wide regions of excess and deficit, respectively, both of relative intensity 0.001 with respect to a uniform flux, superimposed on smaller size structures. The harmonic analysis shows that the large-scale cosmic-ray relative intensity as a function of R.A. can be described by the first and second terms of a Fouries series. The high event statistics allow the study of the energy dependence of the anistropy, showing that the amplitude increases with energy, with a maximum intensity at 10 TeV, and then decreases while the phase slowly shifts toward lower values of R.A. with increasing energy. The ARGO-YBJ data provide accurate observations over more than a decade of energy around this feature of the anisotropy spectrum.

9pages, 6figures

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• All-Sky Measurement of the Anisotropy of Cosmic Rays at 10 TeV and Mapping of the Local Interstellar Magnetic Field
• Progress in high-energy cosmic ray physics
• High-Energy Galactic Cosmic Rays (Astro2020 Science White Paper)
• A Three-component Model for Cosmic-ray Spectrum and Dipole Anisotropy
• EAS age determination from the study of the lateral distribution of charged particles near the shower axis with the ARGO-YBJ experiment
• Cosmic-Ray Convection-Diffusion Anisotropy
• Detection of Cosmic Rays from ground: an Introduction