The EM Algorithm for Imaging with Gaps in the Detector Plane

Abstract

γ-ray telescopes based on coded-mask techniques does not give adirect image of the sky sources but its correlation with the mask responsefunction. To obtain an image of the sky sources one has to treatmathematically the detected image, usually by correlating it with areconstruction array (correlation methods). Unfortunately this kindof methods, although quite fast, have some limitations in the reconstructedimage and in handling the real telescope response.To improve these results, several reconstruction methods have been developedand used. In the case of LEGRI (a γ-ray coded-mask telescopedeveloped for the University of Valencia) we have used the EM algorithm,an iterative maximum likelihood algorithm with very good response andwith good handling of the telescope response.