Magnetic Shielding of Soft Protons in Future X-Ray Telescopes: The Case of the ATHENA Wide Field Imager

Marco Barbera, Valentina Fioretti, Simone Lotti, Andreas Von Kienlin, Silvano Molendi, Arne Rau, Andreas Von Kienlin, Claudio Macculi, Andrea Bulgarelli, Mauro Dadina, Norbert Meidinger, Massimo Cappi, Luigi Piro, Teresa Mineo

Risultato della ricerca: Articlepeer review

4 Citazioni (Scopus)

Abstract

Both interplanetary space and Earth’s magnetosphere are populated by low-energy (≤300 keV) protons that are potentially able to scatter on the reflecting surface of the Wolter-I optics of X-ray focusing telescopes and reach the focal plane. This phenomenon, depending on the X-ray instrumentation, can dramatically increase the background level, reducing the sensitivity or, in the most extreme cases, compromising the observation itself. The use of a magnetic diverter, deflecting protons away from the field of view, requires a detailed characterization of their angular and energy distribution when exiting the mirror. We present the first end-to-end Geant4 simulation of proton scattering by X-ray optics and the consequent interaction with the diverter field and the X-ray detector assembly, selecting the ATHENA Wide Field Imager as a case study for the evaluation of the residual, soft-proton-induced background. We find that in the absence of a magnetic diverter, protons are indeed funneled toward the focal plane, with a focused non-X-ray background well above the level required by ATHENA science objectives (5 × 10‑4 counts cm‑2 s‑1 keV‑1), for all the plasma regimes encountered in both L1 and L2 orbits. These results set the proton diverter as a mandatory shielding system on board the ATHENA mission and all high throughput X-ray telescopes operating in the interplanetary space. For a magnetic field computed to deflect 99% of the protons that would otherwise reach the WFI, Geant4 simulations show that this configuration, in the assumption of a uniform field, would efficiently shield the focal plane, yielding a residual background level of the order or below the requirement.
Lingua originaleEnglish
Numero di pagine11
RivistaTHE ASTROPHYSICAL JOURNAL
Volume867
Stato di pubblicazionePublished - 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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