  Low energy protons (<100-300 keV) in the Van Allen belt and the outer regions
can enter the field of view of X-ray focusing telescopes, interact with the
Wolter-I optics, and reach the focal plane. The use of special filters protects
the XMM-Newton focal plane below an altitude of 70000 km, but above this limit
the effect of soft protons is still present in the form of sudden flares in the
count rate of the EPIC instruments, causing the loss of large amounts of
observing time. We try to characterize the input proton population and the
physics interaction by simulating, using the BoGEMMS framework, the proton
interaction with a simplified model of the X-ray mirror module and the focal
plane, and comparing the result with a real observation. The analysis of ten
orbits of observations of the EPIC/pn instrument show that the detection of
flares in regions far outside the radiation belt is largely influenced by the
different orientation of the Earth's magnetosphere respect with XMM-Newton's
orbit, confirming the solar origin of the soft proton population. The Equator-S
proton spectrum at 70000 km altitude is used for the proton population entering
the optics, where a combined multiple and Firsov scattering is used as physics
interaction. If the thick filter is used, the soft protons in the 30-70 keV
energy range are the main contributors to the simulated spectrum below 10 keV.
We are able to reproduce the proton vignetting observed in real data-sets, with
a 50\% decrease from the inner to the outer region, but a maximum flux of 0.01
counts cm-2 s-1 keV-1 is obtained below 10 keV, about 5 times lower than the
EPIC/MOS detection and 100 times lower than the EPIC/pn one. Given the high
variability of the flare intensity, we conclude that an average spectrum, based
on the analysis of a full season of soft proton events is required to compare
Monte Carlo simulations with real events.

Instrumentation and Methods for Astrophysics