The epicspeccombine is a SAS implementation of the “Combining the spectra of the 3 EPIC cameras” thread that can be found on the XMM-Newton web site. 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 to 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 their own files, but in this case, the user has to ensure that the spectral files have a common spectral range and common binning. 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. If this is not the case then the background merged from different instruments will not be accurate.
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. Meaning that epicespeccombine assumes that the first source spectrum, first background spectrum, first ARF and first RMF go together. The same for the second files etc.
