Background study of the Imaging X-ray Polarimetry Explorer (IXPE)

The next NASA Small Explorer (SMEX) mission, IXPE ( Imaging X-ray Polarimetry Explorer), will be launched in 2021, with three identical X-ray mirror module assemblies and detector units. IXPE introduces the capability for X-ray polarimetric imaging, uniquely enabling the measurement of X-ray polarisation with scientifically meaningful spatial, spectral, and temporal resolution. The background of the focal plane detector based on the Gas Pixel Detector are expected to be negligible for point source observation, but for faint extended source, which will perform X-ray polarimetric imaging for the first time, background should be dealt with carefully. The initial estimates of background rate comes from extrapolations of measurements by gaseous detectors flown on the OSO-8 mission, here we present a result of detailed Geant4 Monte Carlo simulation of the expected inflight background for IXPE. Our simulations include a mass model of the spacecraft and detailed design of the detector; moreover, it will be presented optimised background rejection methods.