Geomagnetic Field Effects on the Imaging Air Shower Cherenkov Technique

TL;DR

This paper investigates how the Earth's geomagnetic field influences the development and detection of gamma-ray induced air showers in Imaging Air Cherenkov Telescopes, affecting gamma-ray discrimination and measurement accuracy.

Contribution

It provides detailed Monte Carlo simulation results for the MAGIC telescope site, highlighting the impact of geomagnetic effects on gamma-ray observations.

Findings

Geomagnetic field affects air shower development.

Gamma-ray detection efficiency is systematically influenced.

Measurements of Crab nebula gamma-rays are impacted by geomagnetic effects.

Abstract

Imaging Air Cherenkov Telescopes (IACTs) detect the Cherenkov light flashes of Extended Air Showers (EAS) triggered by very high energy (VHE) gamma-rays impinging on the Earth's atmosphere. Due to the overwhelming background from hadron induced EAS, the discrimination of the rare gamma-like events is rather difficult, in particular at energies below 100 GeV. The influence of the Geomagnetic Field (GF) on the EAS development can further complicate this discrimination and, in addition, also systematically affect the gamma efficiency and energy resolution of an IACT. Here we present the results from dedicated Monte Carlo (MC) simulations for the MAGIC telescope site. Additionally we show that measurements of sub-TeV gamma-rays from the Crab nebula are affected even for a low GF strength of less than 33 micro Tesla.