In 2005 the XMM-Newton EPIC Background Working Group was founded as a steering and supervising committee to provide the user with clear information on the EPIC background and (SAS)-tools to treat the background correctly for various scenarios. Current progress of this working group can be monitored at the Background Analysis page (EPIC section).
The EPIC background can be divided into two parts: a cosmic X-ray background (CXB), and an instrumental background. The latter component may be further divided into a detector noise component, which becomes important at low energies (i.e. below 300 eV) and a second component which is due to the interaction of particles with the structure surrounding the detectors and the detectors themselves. This component is characterised by a flat spectrum and is particularly important at high energies (i.e. above a few keV).
The particle induced background can be divided into 2 components: an external `flaring' component, characterised by strong and rapid variability, which is often totally absent and a second more stable internal component. The flaring component is currently attributed to soft protons ( smaller than a few 100 keV), which are presumably funnelled towards the detectors by the X-ray mirrors. The stable component is due to the interaction of high-energy particles ( larger than some 100 MeV) with the structure surrounding the detectors and possibly the detectors themselves.
A table summarising the temporal, spectral and spatial properties of the EPIC background components is available at http://www.star.le.ac.uk/amr30/BG/BGTable.html.
The SOC has performed an analysis of the behaviour of the XMM-Newton background from the beginning of the mission (available as XMM-SOC-GEN-TN-0014). Main conclusions are: