Earth magnetic field effects on the cosmic electron flux as background for Cherenkov Telescopes at low energies

TL;DR

This paper investigates how Earth's magnetic field influences low-energy cosmic electrons and positrons, affecting background rates in Cherenkov telescopes, using advanced geomagnetic models and site-specific analyses.

Contribution

It introduces a detailed study of geomagnetic effects on low-energy cosmic electrons using realistic magnetic field models and site-specific considerations for Cherenkov telescopes.

Findings

Geomagnetic field reduces low-energy electron flux at telescope sites.

Site location significantly impacts electron background suppression.

Analysis of 5@5 array demonstrates geomagnetic effects on detection sensitivity.

Abstract

Cosmic ray electrons and positrons constitute an important component of the background for imaging atmospheric Cherenkov Telescope Systems with very low energy thresholds. As the primary energy of electrons and positrons decreases, their contribution to the background trigger rate dominates over protons, at least in terms of differential rates against actual energies. After event reconstruction, this contribution might become comparable to the proton background at energies of the order of few GeV. It is well known that the flux of low energy charged particles is suppressed by the Earth's magnetic field. This effect strongly depends on the geographical location, the direction of incidence of the charged particle and its mass. Therefore, the geomagnetic field can contribute to diminish the rate of the electrons and positrons detected by a given array of Cherenkov Telescopes. In this work we study the propagation of low energy primary electrons in the Earth's magnetic field by using the backtracking technique. We use a more realistic geomagnetic field model than the one used in previous calculations. We consider some sites relevant for new generations of imaging atmospheric Cherenkov Telescopes. We also study in detail the case of 5@5, a proposed low energy Cherenkov Telescope array.