Influence of Earth-Directed Coronal Mass Ejections on the Sun's Shadow Observed by the Tibet-III Air Shower Array

Abstract

We examine the possible influence of Earth-directed coronal mass ejections (ECMEs) on the Sun's shadow in the 3~TeV cosmic-ray intensity observed by the Tibet-III air shower (AS) array. We confirm a clear solar-cycle variation of the intensity deficit in the Sun's shadow during ten years between 2000 and 2009. This solar-cycle variation is overall reproduced by our Monte Carlo (MC) simulations of the Sun's shadow based on the potential field model of the solar magnetic field averaged over each solar rotation period. We find, however, that the magnitude of the observed intensity deficit in the Sun's shadow is significantly less than that predicted by MC simulations, particularly during the period around solar maximum when a significant number of ECMEs is recorded. The ${\chi }^2$ tests of the agreement between the observations and the MC simulations show that the difference is larger during the periods when the ECMEs occur, and the difference is reduced if the periods of ECMEs are excluded from the analysis. This suggests the first experimental evidence of the ECMEs affecting the Sun's shadow observed in the 3~TeV cosmic-ray intensity.

arXiv comment11 pages, 3 figures, accepted for publication in the ApJ

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• EPOS LHC : test of collective hadronization with LHC data
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• Multi-Tev Gamma-Ray Observation from the Crab Nebula Using the Tibet-III Air Shower Array Finely Tuned by the Cosmic-Ray Moon's Shadow
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• Measurements of the Time-Dependent Cosmic-Ray Sun Shadow with Seven Years of IceCube Data -- Comparison with the Solar Cycle and Magnetic Field Models
• Cosmic-ray propagation around the Sun: investigating the influence of the solar magnetic field on the cosmic-ray Sun shadow
• Monitoring the daily variation of Sun-Earth magnetic fields using galactic cosmic rays
• Transient Large-Scale Anisotropy in TeV Cosmic Rays due to an Interplanetary Coronal Mass Ejection