Modeling the in-orbit Background of PolarLight

Abstract PolarLight is a gas pixel X-ray polarimeter mounted on CubeSat, which was launched into Sun-synchronous orbit in 2018 October. We build mass model of the whole CubeSat with Geant4 toolkit to simulate background induced by cosmic (CXB) and high-energy charged particles orbit. The simulated energy spectra morphologies event images both suggest that measured dominated electrons, minor contribution from protons CXB. simulation reveals that, range 2–8 keV, roughly 28% events are caused deposited secondary electron an few physical process identical detection X-rays. Thus, this fraction cannot be discriminated events. distribution uneven detector plane, enhancement near edges. edge effect occurs because electrons tend produce long tracks, discarded readout electronics unless partially internal rate expected around 6 × 10 −3 counts s −1 cm −2 at keV if effective particle discrimination algorithm can applied. This indicates should negligible for future focusing polarimeters focal size order millimeters.