The task rgscombine can be used to combine two or more spectra from one or more sources that have been produced by rgsproc for the same order into a single spectrum and to calculate the corresponding combined response matrix. In order for the task to run, the component spectra must have been calculated by rgsproc on a fixed wavelength grid (the rgsproc default). This method maintains proper counting statistics and has replaced earlier techniques. Refer to the SAS web pages section on individual tasks for more information,
http://xmm-tools.cosmos.esa.int/external/sas/current/doc/rgscombine.