Abstract
The fluorescence detector technique is using the atmosphere as a calorimeter. Besides the precise monitoring of the parameters of the atmosphere a proper knowledge of the optical properties in the UV range of all optical components involved in the measurements of the fluorescence light is vital. Until now, the end-to-end calibration was performed with a 4.5 m2 large, uniformly lit light source attached to the aperture of the telescopes. To improve the maintainability we propose an alternative setup where a small and lightweight light source of known optical properties re-samples the measurement of the big light source piece by piece. This will be achieved by moving the light source based on an integrating sphere in two dimensions in front of the aperture. A prototype setup has been installed and we are currently optimizing the parameters of the system and the procedures. The aim is to reduce the effort for the procedure without diminishing the quality of the measurement. First measurements with this setup have already been performed and the measurements of the geometrical and optical properties of the light source are an ongoing activity. We present our calibration scheme and the first, preliminary results.
Highlights
The fluorescence detector (FD) of the Pierre Auger Observatory [1] consists of 27 fluorescence telescopes at 4 different sites [2], [3] overlooking an area of 3000 km2 equipped with over 1600 water Cherenkov detectors
We are proposing a new type of absolute calibration system which consists of a portable and time stable light source which can be utilized for a fast absolute calibration measurement
It turned out that the differences between the two sets of measurements were of the order of 1 %, already corrected by the aging effect of the photo multipliers tubes (PMTs) of the FD
Summary
The fluorescence detector (FD) of the Pierre Auger Observatory [1] consists of 27 fluorescence telescopes at 4 different sites [2], [3] overlooking an area of 3000 km equipped with over 1600 water Cherenkov detectors. The FD measures the fluorescence light of extensive air showers on clear, moonless nights. For the FD of the Pierre Auger Observatory various systems are used to monitor the variability of the atmosphere and the relative night-to-night changes of the FD. In addition and for obvious reasons it is desirable though not very practical that after any change of components either of an FD telescope or one of its relative calibration system a new absolute calibration should be performed rather close in time in order to get a new reference calibration. The resulting gap after a change in components was bridged in the past by relying on the stability of the relative calibration system and adjusting the calibration constants in a suitable way
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