Analysis of extended sources is complex, challenging and time-consuming. There is currently neither an official SAS recipe, nor a simple thread. Several groups were/are independently working in this field. The XMM-Newton EPIC Background Working Group (BGWG) was therefore founded in 2005 as a steering and supervising committee to provide the users with clear information on the EPIC Background and (SAS)-tools to treat the background correctly for various scenarios.
A dedicated Background Analysis web page is available at
http://xmm.esac.esa.int/external/xmm_sw_cal/background/
with
information and tools collected and documented by the Background Working Group:
A main problem in the analysis of extended sources is that often no statistically useful blank background region can be defined in the observational field-of-view. A workaround is to make use of the provided 'blank sky' background files to generate background spectra corresponding to the camera/mode/filter combination rescaled to the actual observation.
An alternative approach is to model the background spectra based on the background conditions of the indivual observation under study: The recommended method is to make use of the Extended Source Analysis Software (XMM-ESAS) package. This tool is available at http://xmm.esac.esa.int/external/xmm_sw_cal/background/epic_esas.shtml and allows to model the quiescent particle background both spectrally and spatially for the MOS detectors (support for pn is planned for the near future). XMM-ESAS produces background spectra for user-defined regions of the detectors and background images.
Further details are available from the Background Analysis web page and from
a dedicated SAS Workshop presentation at
http://xmm.esac.esa.int/external/xmm_sw_cal/sas_workshop/sas_ws7_files/presentations.shtml