Abstract
The future ground-based gamma-ray observatory, the Cherenkov Telescope Array (CTA) will require reliable monitoring of the atmosphere which is an inherent part of the detector. We discuss here the implementation of the extended method of the Cherenkov Transparency Coeffcient for the atmospheric calibration for the CTA. The method estimates the atmospheric transmission of Cherenkov light, relying on the measurement of the rates of cosmic ray-induced air showers that trigger different pairs of telescopes. We examine the performance of our approach utilizing Monte Carlo simulations assuming various atmospheric conditions and CTA observation configurations.
Highlights
Imaging atmospheric Cherenkov telescopes (IACTs) detect Cherenkov light emitted from air showers of relativistic particles initiated by very-high-energetic (VHE; ≥ 20 GeV) γ-rays of astrophysical origin
We examine the sensitivity of the extended Cherenkov Transparency Coefficient (CTC) method to the variations in the aerosol concentrations and molecular density profiles using Monte Carlo (MC) simulations of the protoninitiated air showers observed by the Cherenkov Telescope Array (CTA)
We presented the extended CTC method for the monitoring of the atmospheric transparency to Cherenkov light in the extensive arrays of IACTs
Summary
Imaging atmospheric Cherenkov telescopes (IACTs) detect Cherenkov light emitted from air showers of relativistic particles initiated by very-high-energetic (VHE; ≥ 20 GeV) γ-rays of astrophysical origin. The development of the air shower and the emission of Cherenkov light are affected by the molecular density profile of the Earth’s atmosphere along the shower direction [1, 2]. Cherenkov photons can be further attenuated in the air through the absorption and scattering on molecules, aerosols and clouds [3, 4]. These atmospheric effects contribute to the uncertainty on the reconstruction of primary particles’ energies and the effective area of the instrument. Among the foreseen calibration approaches is the method of the Cherenkov Transparency Coefficient (CTC) for the monitoring of the atmospheric transparency to Cherenkov light, T ∝ exp(−τ), where τ is the aerosol optical depth.
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