On the optimal characteristics of the multichannel imaging camera for TeV gamma ray observations

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Abstract
The detection efficiency of atmospheric Cerenkov flashes as a function of the camera parameters was studied in order to determine the optimal camera parameters for the discovery of VHE gamma ray point sources. Simulations of the detection process and calculation of the flash parameters are used. It is shown that the optimal value of the camera angular diameter is in the range 3.1 degrees -3.7 degrees and the optimal pixel size is from 0.2 degrees to 0.3 degrees . In these cases the number of photomultipliers ranges from 61 to 127 for a camera with a hexagonal window. The computations are made for the case when any two channels generate a logical signal, i.e. at least two pulses are higher than the threshold. Note that the photocathode current fluctuation caused by the night sky radiation is very important for the calculations because it is the major factor which determines the lower limit for the pixel size. Calculations neglecting fluctuations caused by the night sky lead to an incorrect conclusion: the smaller the pixel size, the better are the images, i.e. they are close to real ones (unlimited resolution camera).