Evaluation of the ATHENA/WFI instrumental background

The Wide Field Imager (WFI) is one of two focal plane instruments of the Advanced Telescope for High-Energy Astrophysics (Athena), ESA’s next large X-ray observatory, planned for launch in the early 2030’s. In the aimed orbit, a halo orbit around L2, the second Lagrange point of the Sun-Earth system the radiation environment, mainly consisting of solar and cosmic protons, electrons and He-ions, could affect the science performance. Furthermore as additional contribution the unfocused hard X-ray background is taken into account. It is important to understand and estimate the expected instrumental background and to investigate measures, like design modifications or analysis methods, which could improve the expected background level in order to achieve the challenging scientific requirement of −3 cts/cm 2 /keV/s. For that purpose, the WFI background working group is investigating possible approaches, which will also be subject to technical feasibility studies. Finally an estimate of the WFI instrumental background for a proposed combination of design optimization and background rejection algorithm is given, showing that WFI is compliant with science background requirements.