The Influence of Sun's and Moon's Shadows on Cosmic-Ray Anisotropy

TL;DR

This paper evaluates how the Sun's and Moon's shadows affect cosmic-ray anisotropy measurements, finding their influence negligible in sidereal time but potentially significant in solar time, serving as a validation benchmark.

Contribution

It provides a detailed calculation of shadow effects on cosmic-ray anisotropy, clarifying their impact and establishing a benchmark for future measurements.

Findings

Shadow effects are negligible in local sidereal time.

Shadow-induced deficits are comparable to solar anisotropy in local solar time.

Shadow effects can serve as validation benchmarks for future experiments.

Abstract

Large-scale anisotropy, with amplitudes reaching approximately 0.1% at TeV energies, has been observed by multiple cosmic-ray experiments. The obstruction of cosmic rays by the Sun and Moon creates shadow effects, potentially impacting the observed cosmic ray anisotropy. To evaluate these effects, this study calculates the contributions of the Sun's and Moon's shadows to the overall cosmic-ray anisotropy in both local solar and sidereal time. The analysis reveals that in local sidereal time, the total 1D projection amplitude of the anisotropy is around 0.003%, which is significantly smaller than the observed cosmic-ray anisotropy. This indicates that the influence of the Sun's and Moon's shadows on cosmic-ray anisotropy analysis in local sidereal time is negligible. In contrast, in local solar time, the shadow-induced deficit appears in a very small time bin, with a magnitude comparable to that of the cosmic-ray solar anisotropy. This deficit could serve as a benchmark for validating anisotropy measurements in future facilities.