Background rejection using image residuals from large telescopes in imaging atmospheric Cherenkov telescope arrays

TL;DR

This paper proposes a novel background rejection method for IACT arrays by analyzing image residuals, leading to significant improvements in background suppression at high energies without sacrificing gamma-ray efficiency.

Contribution

The paper introduces a residual-based background rejection technique for IACTs that enhances high-energy background suppression without reducing gamma-ray detection efficiency.

Findings

Background rejection improved by a factor of 3-4 above 20 TeV.

Method maintains approximately 90% gamma-ray efficiency.

Effective across all energies above 1 TeV.

Abstract

Identification of Cherenkov light generated by muons has been suggested as a promising way to dramatically improve the background rejection power of Imaging Atmospheric Cherenkov Telescope (IACT) arrays at high energies. However, muon identification remains a challenging task, for which efficient algorithms are still being developed. We present an approach in which, rather than identifying Cherenkov light from muons, we simply consider the presence of Cherenkov light other than the main shower image in IACTs with large mirror area. We show that in the case of the H.E.S.S. array of five telescopes this approach results in background rejection improvements at all energies above 1 TeV. In particular, the rejection power can be improved by a factor $\sim3-4$ at energies above 20 TeV while keeping $\sim90\%$ of the original gamma-ray efficiency.