Faster background determination––a method for gaining time coverage and flux measurement accuracy with Cherenkov telescopes

An improved way of taking off-source data for background determination in Cherenkov telescope (CT) observations is proposed. Generalizing the traditional concept of taking on-source/off-source observations of equal duration (e.g. 30 min ON followed by 30 min OFF), faster background determination permits an off-source observation with the same zenith angle distribution as the on-source observation to be obtained within less time. The method permits the on-source observation time to be maximized without compromising the quality of the background determination. It also increases the signal significance for strong sources. The only modification necessary in the data acquisition is a small change to the tracking algorithm. The only modification necessary in the data analysis is to introduce a time normalization which does not increase the systematic errors. The method could become the normal observing mode for CTs when observing strong sources.