New methods of atmospheric Cherenkov imaging for gamma-ray astronomy. II. The Differential Position method

The non-uniformities in response across the face of an atmospheric Cherenkov imaging telescope camera are considered. Using the observational data from the Whipple Observatory telescope it is shown that these non-uniformities can be quite large. Although this does not adversely affect the sensitivity of the camera when used in the On/Off Tracking-mode, it is significant for the False Source method. A new technique is proposed that characterizes the non-uniformity of the camera and allows it to be corrected. It is then possible to map the gamma-ray sky in the vicinity of the source with greater sensitivity than previous methods. The technique was tested on observational data and its power was demonstrated.