Observation of shadowing of the cosmic electrons and positrons by the Moon with IACT

TL;DR

This paper explores using IACTs, particularly MAGIC, to observe the Moon's shadowing effects on cosmic electrons and positrons, aiming to improve understanding of cosmic-ray spectral anomalies and their origins.

Contribution

It proposes a novel method to distinguish e-, e+, and gamma-ray components via Moon shadowing with IACTs, enhancing the study of cosmic-ray composition at high energies.

Findings

Feasibility of observing e+ and e- shadows with IACTs is discussed.

MAGIC's high altitude and large telescopes are suitable for low-energy threshold observations.

Potential to improve understanding of cosmic-ray spectral anomalies.

Abstract

Recent measurements of the cosmic-ray electron (e-) and positron (e+) fluxes show apparent excesses compared to the spectra expected by standard cosmic-ray (CR) propagation models in our galaxy. These excesses may be related to particle acceleration in local astrophysical objects, or to dark matter annihilation/decay. The e+/e- ratio (measured up to ~100 GeV) increases unexpectedly above 10 GeV and this may be connected to the excess measured in all-electron flux at 300-800 GeV. Measurement of this ratio at higher energies is a key parameter to understand the origin of these spectral anomalies. Imaging Atmospheric Cherenkov Telescopes (IACT) detect electromagnetic air showers above 100 GeV, but, with this technique, the discrimination between primary e-, e+ and diffuse gamma-rays is almost impossible. However, the Moon and the geomagnetic field provide an incredible opportunity to separate these 3 components. Indeed, the Moon produces a 0.5deg-diameter hole in the isotropic CR flux, which is shifted by the Earth magnetosphere depending on the momentum and charge of the particles. Below few TeV, the e+ and e- shadows are shifted at >0.5deg each side of the Moon and the e+, e- and gamma-ray shadows are spatially separated. IACT can observe the e+ and e- shadows without direct moonlight in the field of view, but the scattered moonlight induces a very high background level. Operating at the highest altitude (2200m), with the largest telescopes (17m) of the current IACT, MAGIC is the best candidate to reach a low energy threshold in these peculiar conditions. Here we discuss the feasibility of such observations.