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

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.

To appear in Astroparticle Physics

References in corpus (5)

• Observation of an anomalous positron abundance in the cosmic radiation
• Measurement of separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope
• The cosmic-ray electron flux measured by the PAMELA experiment between 1 and 625 GeV
• Galactic secondary positron flux at the Earth
• Monte Carlo Studies of Geomagnetic Field Effects on the Imaging Air Cherenkov Technique for the MAGIC Telescope Site