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Calibration of a Photometric Filter System with a 5-inch Telescope Subsystem of the MAGIC Telescopes

Marine Pihet

School

Max-Planck-Institute for Physics

Abstract:

In this Bachelor thesis, the photometric calibration of the 5-inch MAGIC Atmosphere Minion (MAM) telescope on the Canary Island of La Palma, Spain, is presented. The telescope is supposed to measure the atmospheric transmission in real time and in point- ing direction of the Major Atmospheric Gamma-Ray Imaging Cherenkov (MAGIC) tele- scopes, also situated on La Palma. Different concepts of photometry are discussed and their suitability is evaluated according to the special observing conditions in which MAM will be operating. These include possibly challenging weather conditions, very large zenith angle observations, and an automatic mode of operation. The task of MAM is motivated by the need to correct MAGIC data for the effect of atmospheric extinction. When a gamma ray enters Earth’s atmosphere it produces an electromagnetic air shower of secondary particles, which can be observed by MAGIC be- cause of the Cherenkov radiation they emit. Knowledge about the amount of Cherenkov light surviving the way through the atmosphere is crucial for the correct reconstruc- tion of the primary gamma-ray energy. MAM is equipped with two telescope tubes, a spectrograph, and several cameras for imaging. Only the 5-inch telescope and a CMOS camera were used for this Bachelor work. The calibration measurement was done re- motely during good weather conditions. Five stars with a wide range of color indices were observed in the l, r, g, and b filter from the Baader company and at different zenith angles ranging from 28 ◦ to 80 ◦. Existing software and some modules, especially written for the purpose of this thesis, were used for the control of the telescope. From the data, extinction coefficients in different bands of the visible spectrum at the site of the Roque de los Muchachos observatory were calculated and compared to other measurements. They were found to match the expectation and agree with the dependency on wave- length and color of the observed star. As a final result, color transformation relations between the Landolt photometric standard system and the MAM observational system were derived for the filters r, g and b. The results for filter r are found to be inconsis- tent and an attempt is made to explain this. Results for filter g and b are consistent and stable, but precision should be improved to enable more concrete statements. The main conclusion is that more stars are needed to reliably characterise the transformation relations and reduce uncertainties. A reevaluation of the photometric concepts shows that the concept based on an exist- ing catalog of stars has potential for success, but is more complex and susceptible for systematic uncertainties arising from the transformation between photometric systems. The concept based on the MAM observational system is simpler and can give quicker first results with less effort.

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