Atmospheric calibration of the Cherenkov Telescope Array

TL;DR

This paper discusses the importance of atmospheric calibration for the Cherenkov Telescope Array, emphasizing the need for monitoring atmospheric conditions to improve gamma-ray observations and reduce systematic uncertainties.

Contribution

It presents procedures and strategies for atmospheric monitoring and calibration tailored for CTA, including the deployment of monitoring devices at the sites.

Findings

Atmospheric conditions significantly impact CTA observations.

Monitoring aerosol and molecular profiles improves calibration accuracy.

Preparedness of atmospheric data enhances observation efficiency.

Abstract

Atmospheric monitoring is an integral part of the design of the Cherenkov Telescope Array (CTA), as atmospheric conditions affect the observations by Imaging Atmospheric Cherenkov Telescopes (IACT) in multiple ways. The variable optical properties of the atmosphere are a major contribution to the systematic uncertainty in the determination of the energy and flux of the gamma photons. Both the development of the air-shower and the production of Cherenkov light depend on the molecular profile of the atmosphere. Additionally, the rapidly changing aerosol profile, affecting the transmission of the Cherenkov light, needs to be monitored on short time scales. Establishing a procedure to select targets based on current atmospheric conditions can increase the efficiency of the use of the observation time. The knowledge of atmospheric properties of the future CTA locations and their annual and short-term variations in advance is essential so that the atmospheric calibration can be readily applied to first scientific data. To this end, some devices are already installed at one or both of the selected sites...