PoS - Proceedings of Science
Volume 444 - 38th International Cosmic Ray Conference (ICRC2023) - Gamma-ray Astronomy (GA)
Correcting for atmospheric variations in IACT data analyses
T.L. Holch
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Pre-published on: August 05, 2023
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A fundamental concept of atmospheric Cherenkov detectors is the use of the Earth's atmosphere as calorimeter. Apart from the advantages of employing this large existing air volume as part of a detector, this implies an accurate characterisation of the atmospheric conditions to correctly interpret the collected data. As extensive Monte Carlo simulations form the basis for common data analyses of such instruments, it can be unpractical and computationally expensive to adequately cover the full phase space of possible conditions under which measurements are performed. Often, this is resolved by excluding data that was taken under non-favourable conditions from an analysis. To avoid discarding valuable data, a scheme to correct for deviations between simulated and actual atmospheric conditions is presented in this contribution. The proposed scheme employs atmospheric data from various sources to build refined atmospheric models. The transmission profile used in MC simulations is then compared to a range of transmission profiles for conditions under which observations were conducted. By applying parametrised air-shower profiles, event-wise zenith and energy dependent correction factors can be determined to refine particle energies and instrument response functions without the need to rerun the full MC simulation chain. A proof of concept is shown on the example of observations of the Crab Nebula with the imaging atmospheric Cherenkov telescopes (IACTs) of the H.E.S.S. experiment with a focus on varying aerosol levels. The scheme can, however, be adapted to correct for the influence of various atmospheric parameters.
DOI: https://doi.org/10.22323/1.444.0779
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