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Abstract:
Imaging atmospheric Čerenkov telescopes are complex instruments that use Earth's atmosphere as an integral part of the detector system. For the eight years of observations with the High Energy Stereoscopic System (H.E.S.S.) in Namibia, we study the long-term behaviour of the quality criteria used to select data taken under good atmospheric conditions and in the absence of hardware problems. The overall yield in Čerenkov photons varies strongly with time for H.E.S.S., due to degradation of mirrors and natural and man-made variations of atmospheric transparency, on time scales from hours to seasons. We present robust cuts that cope with these effects over the full dataset of H.E.S.S. and examine the influence of the cuts on energy reconstruction and spectral parameters.
