The epicspeccombine is a SAS implementation of the “Combining the spectra of the 3 EPIC cameras” thread that can be found at http://xmm.esac.esa.int/sas/current/documentation/threads/epic_merging.shtml. For convenience, this task should be used in combination with multixmmselect and multiespecget tasks.
epicspeccombine task requires as an input a set of source spectra, background spectra, plus the corresponding response and effective area files of the three EPIC cameras as produced by the multiespecget. Although, it is not mandatory the use of multiespecget task prior epicespeccombine execution, it is highly recommended because multiespecget task sets accordingly all the parameters related to spectral range or energy binning. Nevertheless, the user can use his own files, but in this case, the user has to ensure that the spectra files have a common spectral range and a common binnig. Also, the user has to provide the response and ancilliary files with the same energy binning.
epicspeccombine task assumes that the spectral extraction regions are identical for all the EPIC input files.
Firstly, this task merges together the source+background and background spectra files into a single set of merged source+background spectrum and background spectrum. Then, the redistribution matrix and effective area vector files are also combined together into a single response file.
The files for each of the input parameters: pha, bkg, rmf and arf have to be introduced in order. Its means, epicespeccombine assumes that the order of the input list is the same and it is correct.
The algorithm, together with the weights used to combine the response files are properly described in the SAS thread web page.
