Systematic effects induced on IBIS detectors by background and inhomogeneity of the spatial response

The spatial distribution of the background events may affect the source detection capability of IBIS at high energies (>200 keV) for both ISGRI and PICsIT layers. The observed background is found to be variable and spatially structured, and in some cases its properties strongly deviate from the expected statistical behaviour. Background correction methods are then necessary to improve the quality of the shadowgrams obtained from sources. In order to perform an efficient flat-fielding the response of the detector to both source (y-rays) and background events is investigated using data from Monte Carlo simulations and in-flight calibration observations.