Research on the On-orbit Background of the Hard X-Ray Imager Onboard ASO-S

The space environment background of various particle fluxes of the Hard X-ray Imager (HXI), one of the payloads of the Advanced Space-based Solar Observatory (ASO-S) spacecraft, is investigated and presented. Different approaches are used to obtain the input information on various space environment particles (protons, alpha particles, electrons, positrons, neutrons, and photons). Some special regions (SAA and radiation belt) are also taken into account. The findings indicate that electrons are the primary background source in the radiation belt. Due to the large background flux generated by electrons, HXI cannot effectively observe solar flares in the radiation belt. Outside the radiation belt, primary protons and albedo photons are the main sources of background at low and high magnetic latitudes respectively. The statistical analysis of the flare and background spectra shows that the errors of the flare energy spectrum observation are mainly concentrated in the high energy band, and the detector still has a certain spectrum observation capability for flares of C-class and below in the low energy band of the non-radiation belt. The imaging observation of flares of C-class and below is significantly affected by the accuracy of background subtraction. The energy band with the best signal-to-noise ratio is from 10 to 50 keV, which can be used to monitor the formation and class of flares.