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A  BACKGROUND  EVENT



Cosmic radiation (single muon or soft component) passing through the FD camera can produce a geometrically and time correlated signals on several pixels. This can be due to Cherenkov light produced in the glass of the photomultipliers. In this event a nice track is observed on the camera. On the left side the active pixels are shown in green. The black dots indicate the pixels whose FADC traces are shown on the histograms on the right side (bin equal to 100 ns).

 Notice that all signals appear at the same time as expected for a cosmic ray passing through the camera.   Events of this kind are observed also when the shutters of the telescopes are closed.

Events due to a cosmic ray shower in the atmosphere  show a completely different  pattern  in the FADC traces  (see previous event).







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