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Detailed Characterization of the Performance of the MAGIC LIDAR Using a 7-year Dataset

Felix Schmuckermaier


Technische Universität München


The Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes are a system of two Imaging Atmospheric Cherenkov Telescopes (IACTs) located at the Roque de Los Muchachos Observatory, on the Canary island of La Palma at an altitude of 2200 m. With a mirror diameter of 17 m, MAGIC is able to observe gamma radiation between 50 GeV and 50 TeV, making it one of the leading experiments in the field of ground-based gamma-ray astronomy. IACTs make calorimetric use of Earth’s atmosphere, which allows these instruments to reach effective areas in the order of km 2 , but also makes them strongly dependent on the quality of the atmosphere at the time of the observations. Changes in the atmospheric conditions due to clouds or dust can affect the shape and brightness of the shower images detected in the telescope cameras, which ultimately can lead to a wrong reconstruction of the gamma-ray data. In order to mitigate this problem, the MPP group built and has been operating a single wavelength elastic LIDAR (LIght Detection And Ranging) system, located next to the MAGIC telescopes, to perform real time ranged-resolved measurements of the atmospheric transmission. This information is then used to quantify the quality of the telescope data, as well as to correct the data taken under suboptimal atmospheric conditions. This work presents a detailed characterization of the correction capabilities of the LIDAR system. This is obtained through a dedicated set of analyses scripts that permit an automated and uniform determination of the accuracy of the applied LIDAR corrections on data from the Crab Nebula spanning over seven years. The study reports the LIDAR performance for a variety of atmospheric conditions and for two different strategies to correct the gamma-ray data. The MAGIC telescopes are currently the only operational IACT using a LIDAR system, and hence this pioneering work will have a positive impact on the performance of MAGIC, and also in that of future Cherenkov telescopes, such as CTA.

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