XMM-Newton Science Analysis System: User Guide

6.2.3 Handling of corrections applied to image mode data

As pointed out before, an observation with OM may be composed of several exposures which contain different observed windows. There are three final data products per observed science window (OSW), namely IMAGE_.FIT, SIMAGE.FIT and SWSRLI.FIT. Two additional products, FLAFLD.FIT and OBSMLI.FIT, are generated on a per observation basis. The task omichain loops over all image mode data files of all exposures in an observation. The following tasks are applied to each individual observation window.

• omprep (step4). The task omprep copies the raw images into an intermediate output file. It adds several keywords to this intermediate output file. Although this file is not a final data product, it is carried forward within the processing of OM image data and ends up being contained in the final IMAGE_ product.

• omcosflag (step5). The task omcosflag generates a quality map. Bad pixels are flagged taking also into account the tracking history information. The quality array (bad pixels are flagged as non-zero there) itself is written into the quality extension of the intermediate image files. It is used later by other tasks and it is propagated into the IMAGE_.FIT PPS output file.

• omflatfield (step6). The task omflatfield applies the tracking history file (as contained in the intermediate processing product of the tracking history task) to the OM flatfield file (FLAFLD). The resulting drift corrected flatfield file is applied to the intermediate OM image file. The flatfield corrected OM image is written as an intermediate data product, which is used as an input to ommodmap. Since the current flat field is unity, this correction has no effect on the data.

• ommodmap (step7). The task ommodmap applies the modulo 8 correction to an OM image. The modulo 8 background fluctuations are introduced to an OM image by imperfections of the photon centroiding algorithm. An intermediate image file is generated, which acts as input to the task omdetect.