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

Modeling the in-orbit Background of PolarLight

Nasimi H.;Baldini L.;Bellazzini R.;Spandre G.;Pinchera M.;
2021-01-01

Abstract

PolarLight is a gas pixel X-ray polarimeter mounted on a CubeSat, which was launched into a Sun-synchronous orbit in 2018 October. We build a mass model of the whole CubeSat with the Geant4 toolkit to simulate the background induced by the cosmic X-ray background (CXB) and high-energy charged particles in the orbit. The simulated energy spectra and morphologies of event images both suggest that the background measured with PolarLight is dominated by high-energy electrons, with a minor contribution from protons and the CXB. The simulation reveals that, in the energy range 2-8 keV, roughly 28% of background events are caused by energy deposited by a secondary electron with an energy of a few keV, in a physical process identical to the detection of X-rays. Thus, this fraction of the background cannot be discriminated from X-ray events. The background distribution is uneven on the detector plane, with an enhancement near the edges. The edge effect occurs because high-energy electrons tend to produce long tracks, which are discarded by the readout electronics unless energy is partially deposited near the edges. The internal background rate is expected to be around 6 10-3 counts s-1 cm-2 at 2-8 keV if an effective particle discrimination algorithm can be applied. This indicates that the internal background should be negligible for future focusing X-ray polarimeters with a focal size of the order of millimeters.
2021
Huang, J.; Feng, H.; Li, H.; Long, X.; Yang, D.; Zeng, W.; Wu, Q.; Jiang, W.; Minuti, M.; Costa, E.; Muleri, F.; Citraro, S.; Nasimi, H.; Yu, J.; Jin,...espandi
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/1132158
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 3
  • ???jsp.display-item.citation.isi??? 3
social impact