An efficient method for reducing the background of microcalorimeters applied to ATHENA-XMS

We present several solutions to reduce the background that will be experienced by the X-ray Microcalorimeter Spectrometer (XMS) aboard of the ATHENA mission due to Galactic Cosmic Rays (GCR) and solar particles present in the second Lagrangian point L2. The configuration presented in this paper is the one adopted for the International X-ray Observatory (IXO) but the derived estimates can be considered a conservative limit for ATHENA, that is the IXO redefined mission proposed to ESA. We used the Geant4 toolkit, a Monte Carlo based simulator, to investigate the rejection efficiency of the anticoincidence system and assess the residual background on the detector. Even though the mission did not pass the down selection of ESA. this work lay the basis of a study for a microcalorimeters-based mission in L2.