In this section, general recommendations for the generation of the appropriate redistribution matrix and auxiliary response file for extended sources are given.
As the response function of the EPIC cameras is spatially dependent, the rmfgen and arfgen tasks need to know how the source flux is distributed within the extraction region. A detector map mechanism, has been adopted for this purpose. Essentially a grid is placed over the source region and the response parameters are calculated at each point and then averaged taking into account the flux distribution. For point sources the flux distribution is that of the point spread function (default setting detmaptype=psf).
Large, non point-like sources should be either approximated by a uniform distribution, setting detmaptype=flat, or modeled accurately by creating an image of the source region. Such a detector map can be created using evselect or xmmselect (see § 4.7). The detector map should entirely cover the region used for extracting the spectrum and should be created with sufficient resolution to sample the variation in flux distribution; a 100 by 100 pixel image may be sufficient. The detector map is supplied to the rmfgen and arfgen tasks by setting
rmfgen spectrumset=<spectrum_name> rmfset=<rmf_name> detmaptype=dataset \
detmaparray=<detector-map_name>
and
arfgen spectrumset=<spectrum_name> arfset=<arf_name> detmaptype=dataset \
detmaparray=<detector-map_name> extendedsource=yes
The task descriptions give further info and provide some examples for the
generation of response matrices for extended sources.