Kavli Affiliate: Catherine E. Grant
| First 5 Authors: Fabio Gastaldello, Martino Marelli, Silvano Molendi, Iacopo Bartalucci, Patrick Kühl
| Summary:
We analyzed the unexposed to the sky outFOV region of the MOS2 detector on
board XMM-Newton covering 15 years of data amounting to 255 Ms. We show
convincing evidence that the origin of the unfocused background in XMM-Newton
is due to energetic protons, electrons and hard X-ray photons. Galactic Cosmic
Rays are the main contributors as shown by the tight correlation (2.6% of total
scatter) with 1 GeV protons data of the SOHO EPHIN detector. Tight correlations
are found with a proxy of the Chandra background rate, revealing the common
source of background for detectors in similar orbits, and with the data of the
EPIC Radiation Monitor (ERM), only when excluding Solar Energetic Particles
events (SEPs). The entrance to the outer electron belts is associated to a
sudden increase in the outFOV MOS2 rate and a spectral change. These facts
support the fact that MeV electrons can generate an unfocused background
signal. The correlation between MOS2 outFOV data and the SOHO EPHIN data
reveals a term constant in time and isotropic similar to the one found in the
study of the pn data. The most plausible origin of this component is hard
unfocused X-ray photons of the Cosmic X-ray Background (CXB) Compton-scattering
in the detector as supported by the strength of the signal in the two detectors
with different thicknesses. Based on this physical understanding a particle
radiation monitor on board ATHENA has been proposed and it is currently under
study. It will be able to track different species with the necessary accuracy
and precision to guarantee the challenging requirement of 2% reproducibility of
the background.
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