The output of the OM chains contains brightness values for each source in units of count rates, magnitudes and fluxes. This information can be found in the source list file for each exposure. In addition, as we have seen there is a combined source list containing the brightness values for all exposures within an observation. Consistency checks of observed OM brightnesses with models that fit the X-ray data are thus possible with the combined source list alone.
To facilitate a graphical comparison of OM data with X-ray data in the form of a Spectral Energy Distribution (SED) or to fit a model to the combined X-ray and OM data, the SAS task om2pha produces a file in the OGIP II format that can be read into spectral fitting programs such as Xspec.
A detailed description of om2pha can be found in the OM corresponding thread, Converting OM data to OGIP II format. If OM data are to be analysed in combination with X-ray data, it may be easiest to do a complete run with xmmextractor.