Cosmic-Ray Events as Background in Imaging Atmospheric Cherenkov Telescopes

Abstract

The dominant background for observations of gamma-rays in the energy region above 50 GeV with Imaging Atmospheric Cherenkov telescopes are cosmic-ray events. The images of most of the cosmic ray showers look significantly different from those of gamma-rays and are therefore easily discriminated. However, a small fraction of events seems to be indistinguishable from gamma-rays. This constitutes an irreducible background to the observation of high-energy gamma-ray sources, and limits the sensitivity achievable with a given instrument. Here, a Monte Carlo study of gamma-like cosmic-ray events is presented. The nature of gamma-like cosmic-ray events, the shower particles that are responsible for the gamma-like appearance, and the dependence of these results on the choice of the hadronic interaction model are investigated. Most of the gamma-like cosmic ray events are characterised by the production of high-energy pi0's early in the shower development which dump most of the shower energy into electromagnetic sub-showers. Also Cherenkov light from single muons can mimic gamma-rays in close-by pairs of telescopes. Differences of up to 25% in the collection area for gamma-like proton showers between QGSJet/FLUKA and Sibyll/FLUKA simulations have been found.

Accepted by Journal of Astroparticle Physics

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• Constraints on Cosmic Rays, Magnetic Fields, and Dark Matter from Gamma-Ray Observations of the Coma Cluster of Galaxies with VERITAS and Fermi
• Discovery of VHE $\gamma$-ray emission from the SNR G54.1+0.3
• Systematic uncertainties in air shower measurements from high-energy hadronic interaction models
• Detection of extended gamma-ray emission around the Geminga pulsar with H.E.S.S
• A spatial likelihood analysis for MAGIC telescope data
• Nature of the low-energy, γ-like background for the Cherenkov Telescope Array
• Detection prospects of very and ultra high-energy gamma rays from extended sources with ASTRI, CTA, and LHAASO
• Effect of the uncertainty in the hadronic interaction models on the estimation of the sensitivity of the Cherenkov Telescope Array
• Muons as a tool for background rejection in Imaging Atmospheric Cherenkov Telescope arrays
• Estimation of the height of the first interaction in gamma-ray showers observed by Cherenkov telescopes
• The background from single electromagnetic subcascades for a stereo system of air Cherenkov telescopes