Atmospheric monitoring and array calibration in CTA using the Cherenkov Transparency Coefficient

TL;DR

This paper explores extending the Cherenkov Transparency Coefficient (CTC) method from H.E.S.S. to the more complex CTA for atmospheric monitoring and telescope calibration, aiming to reduce systematic uncertainties in gamma-ray observations.

Contribution

It presents the first feasibility study of applying the CTC technique to CTA for atmospheric monitoring and inter-calibration of telescopes.

Findings

Initial results indicate potential for CTC extension to CTA.

Challenges due to CTA's complexity and diverse telescope cameras.

Feasibility of using CTC for improved calibration and atmospheric monitoring.

Abstract

The Cherenkov Telescope Array (CTA) will be the next generation observatory employing different types of Cherenkov telescopes for the detection of particle showers initiated by very-high-energy gamma rays. A good knowledge of the Earth's atmosphere, which acts as a calorimeter in the detection technique, will be crucial for calibration in CTA. Variations of the atmosphere's transparency to Cherenkov light and not correctly performed calibration of individual telescopes in the array result in large systematic uncertainties on the energy scale. The Cherenkov Transparency Coefficient (CTC), developed within the H.E.S.S. experiment, quantifies the mean atmosphere transparency ascertained from data taken by Cherenkov telescopes during scientific observations. Provided that atmospheric conditions over the array are uniform, transparency values obtained per telescope can be also used for the calibration of individual telescope responses. The application of the CTC in CTA presents a challenge due to the greater complexity of the observatory and the variety of telescope cameras compared with currently operating experiments, such as H.E.S.S. We present here the first results of a feasibility study for extension of the CTC concept in CTA for purposes of the inter-calibration of the telescopes in the array and monitoring of the atmosphere.