comb combines the various EPIC images from a single observation (ObsID), including images from multiple exposures, into single count, exposure, model particle background, and soft proton background images.
comb compensates for the inclusion of observations with different filters in the mosaic. It uses the results of PIMMS with the assumption of a power-law spectrum with photon indecies (alpha) of 2.4, 1.7, and 1.0, and absorption of H I cm. The user enters a vlaue for alpha between 1.0 and 2.4 where 1.0 will select the hard spectrum, 1.7 selects the medium spectrum, and 2.4 selects the soft spectrum. Intermediate values will produce a linear scaling between the two nearest spectra. The exposure image is then scaled by the ratio of the model count rates for the MOS2 medium filter versus the thin or thick, making the resultant image appropriate for the MOS2 medium filter.
Warning and requirements: comb is part of the esas package which has been integrated into SAS. However, it is limited to work within the esas data reduction scheme. This is specially true wrt to the names and structures of the input files. In particular, comb assumes that another tasks from the package, mos-spectra / pn-spectra, mos_back / mos_back and rot-im-det-sky, have been successfully run for the exposures to be used.