The Origin of the Unfocused XMM-Newton Background, Its Variability, and Lessons Learned for ATHENA

Abstract We analyzed the unexposed to sky (outFOV) region of MOS2 detector on board XMM-Newton covering 15 yr data amounting 255 Ms. show convincing evidence that origin unfocused background in is due energetic protons, electrons, and hard X-ray photons. Galactic cosmic rays are main contributors as shown by tight correlation (2.6% total scatter) with 1 GeV proton SOHO EPHIN detector. Tight correlations found a proxy Chandra rate, revealing common source for detectors similar orbits, EPIC Radiation Monitor, only when excluding Solar particle events. The entrance outer electron belts associated sudden increase outFOV rate spectral change. These facts support fact MeV electrons can generate an signal. between reveals term constant time isotropic, one study pn data. most plausible this component photons Compton scattering supported strength signal two different thicknesses. Based physical understanding, radiation monitor Advanced Telescope High Energy Astrophysics has been proposed it currently under study. It will be able track species necessary accuracy precision guarantee challenging requirement 2% reproducibility background.