The Cherenkov Telescope Array (CTA) is the future ground-based observatory for gamma-ray astronomy at very high energies. The atmosphere is an integral part of every Cherenkov telescope. Different atmospheric conditions, such as clouds, can reduce the fraction of Cherenkov photons produced in air showers that reach ground-based telescopes, which may affect the performance. Decreased sensitivity of the telescopes may lead to misconstructed energies and spectra. This study presents the impact of various atmospheric conditions on CTA performance. The atmospheric transmission in a cloudy atmosphere in the wavelength range from 203 nm to 1000 nm was simulated for different cloud bases and different optical depths using the MODerate resolution atmospheric TRANsmission (MODTRAN) code. MODTRAN output files were used as inputs for generic Monte Carlo simulations. The analysis was performed using the MAGIC Analysis and Reconstruction Software (MARS) adapted for CTA. As expected, the effects of clouds are most evident at low energies, near the energy threshold. Even in the presence of dense clouds, high-energy gamma rays may still trigger the telescopes if the first interaction occurs lower in the atmosphere, below the cloud base. A method to analyze very high-energy data obtained in the presence of clouds is presented. The systematic uncertainties of the method are evaluated. These studies help to gain more precise knowledge about the CTA response to cloudy conditions and give insights on how to proceed with data obtained in such conditions. This may prove crucial for alert-based observations and time-critical studies of transient phenomena.
|Journal||Proceedings of Science|
|State||Published - 18 Mar 2022|
|Event||37th International Cosmic Ray Conference, ICRC 2021 - Virtual, Berlin, Germany|
Duration: 12 Jul 2021 → 23 Jul 2021
Bibliographical noteFunding Information:
The work performed at the University of Łódź was supported by the Narodowe Centrum Nauki grant No. UMO-2016/22/M/ST9/00583. The work at the University of Rĳeka was performed using the supercomputer "Bura" within the Center for Advanced Computing and Modelling. The authors would like to thank CTA Consortium and MAGIC Collaboration for the permission to use their software.
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