The Cherenkov transparency coefficient for the atmospheric monitoring and array calibration at the Cherenkov Telescope Array South

TL;DR

This paper evaluates the Cherenkov transparency coefficient (CTC) as a method for atmospheric monitoring and calibration of telescopes at the Cherenkov Telescope Array South, using simulations to assess its effectiveness under various conditions.

Contribution

It introduces and tests the CTC method for atmospheric and array calibration in CTA South through detailed Monte Carlo simulations, demonstrating its potential effectiveness.

Findings

CTC can reliably estimate atmospheric attenuation.

The method allows for relative calibration of telescope optical throughput.

Feasibility is confirmed across different telescope sizes and atmospheric conditions.

Abstract

Reconstruction of energies of very-high-energy gamma-rays observed by imaging atmospheric Cherenkov telescopes is affected by changes in the atmospheric conditions and the performance of telescope components. Reliable calibration schemes aimed at these effects are necessary for the forthcoming Cherenkov Telescope Array (CTA) to achieve its goals on the maximally allowed systematic uncertainty of the global energy scale. A possible means of estimating the atmospheric attenuation of Cherenkov light is the method of the Cherenkov transparency coefficient (CTC). The CTC is calculated using the telescope detection rates, dominated by the steady cosmic ray background, while properly correcting for the hardware and observational conditions. The coefficient can also be used to relatively calibrate the optical throughput of telescopes on the assumption of homogeneous atmospheric transparency above the array. Using Monte Carlo simulations, we investigate here the potential of the CTC method for the atmospheric monitoring and telescope cross-calibration at the CTA array in the southern hemisphere. We focus on the feasibility of the method for the array of telescopes of three sizes in different observation configurations and under various levels of atmospheric attenuation.