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 mentioned above is available at http://www.cosmos.esa.int/web/xmm-newton/background.
The SOC has performed an analysis of the seasonal and long-term behaviour of the XMM-Newton background from the beginning of the mission (available as XMM-SOC-GEN-TN-0014). Main conclusions are: