A method to improve the visibility of time-variable gamma-ray sources in structured background

For the investigation of time variable gamma-ray sources (e.g. pulsars) embedded in a spatially structured background emission, the spatial selection of those gamma-ray events which are probable to increase the observed signal is not a trivial task. A method is presented which allows for the optimum event selection without introducing any statistical trials which could reduce the significance of the result. In an iterative procedure spatial regions are defined from which gamma rays should be accepted in order to observe the optimum signal from the source. These regions depend on the energy of the probed gamma-ray, on the spatial structure and intensity of the background around the source, on the tentative intensity of the source and on the observing instrument's angular resolution. The method is applied to simulated and observed data to demonstrate its feasibility and merits.