The influence of the Sun and Moon on the observation of very high energy gamma-ray sources using EAS arrays

TL;DR

This paper investigates how the Sun and Moon affect the observation of very high energy gamma-ray sources using ground-based EAS arrays, highlighting their potential to cause observational biases and proposing strategies to mitigate these effects.

Contribution

It introduces a detailed analysis of the Sun and Moon's influence on VHE gamma-ray observations and suggests data analysis strategies to account for their effects.

Findings

Sun and Moon can significantly block gamma-ray signals near their line of sight.

The Sun causes gamma-ray absorption, affecting source detection.

Strategies are proposed to mitigate observational biases caused by celestial bodies.

Abstract

With great advance of ground-based extensive air shower array, such as LHAASO and HAWC, many very high energy (VHE) gamma-ray sources have been discovered and are been monitored regardless of the day and the night. Hence, the Sun and Moon would have some compact on the observation of gamma-ray sources, which have not been taken into account in previous analysis. In this paper, the influence of the Sun and Moon on the observation of very high energy gamma-ray sources when they are near the line of sight of the Sun or Moon is estimated. The tracks of all the known VHE sources are scanned and several VHE sources are found to be very close to the line of sight of the Sun or Moon during some period. The absorption of very high energy gamma-ray by sunlight is estimated with detailed method and some usefully conclusions are achieved. The main influence is the block of the Sun and Moon on gamma-ray and their shadow on the cosmic ray background. The influence is investigated considering the detector angular resolution and some strategy on data analysis are proposed to avoid the underestimation of the gamma-ray emission.