Analysis of data from coded-mask telescopes by maximum likelihood

Abstract Coded mask telescopes have proved of great utility in X- and γ-ray astronomy. A coded mask telescope of a non-cyclic “box-camera” design can in some circumstances have a sensitivity advantage over an optimally coded cyclic configuration, but images reconstructed by a simple correlation technique are subject to various imperfections. A new method, maximum likelihood fitting (MALF), for the analysis of data from non-cyclic coded mask telescopes is presented. MALF avoids artifacts due to strong sources and handles in an optimum way data affected by small-number statistics, by partial coding and by aspects of real systems such as finite detector depth and obscurations of parts of the detector.