Characterization of the Particle-induced Background of XMM-Newton EPIC-pn: Short- and Long-term Variability

Abstract

The particle-induced instrumental background of X-ray observatories is dominated by the highly energetic Galactic Cosmic Ray (GCR) primary protons, electrons, and He ions depositing some of their energy as they pass through the detector. The interactions of these primary particles with the detector housing produce secondary particles that mimic X-ray events from celestial sources and constitute the particle-induced background. We investigate the short and long-term properties of the unfocused particle background of the XMM-Newton EPIC-pn camera taken in the small window mode (SWM), with the filter wheel closed. We then compare the results with the SWM observations of astrophysical sources taken through the thick and thin filters. The long term variability of particle-induced background shows strong modulation with the solar cycle, indicating that this background is mostly dominated by GCRs. We find that valid events within a 30 pixel radius of the particle events are highly correlated with these GCR particle primaries. The spectral properties and branching ratios of valid events show some variation, depending on their origin, i.e., particle-induced or astrophysical sources. These results can be used to characterize and reduce the non-X-ray background in XMM-Newton and future silicon-based X-ray detectors.

Discovery of a supercluster in the eROSITA Final Equatorial Depth Survey: X-ray properties, radio halo, and double relics

“…A4, page 4 of 18 V. Ghirardini et al: eFEDS supercluster We also added extra power-law models and a few Gaussian emission lines to take into account the instrumental background. This component is not folded through the ARF file as the highly energetic cosmic-ray (CR) particles do not get focused through the telescope mirror (Bulbul et al 2020). The shape of the instrumental background has been fixed to the values obtained from the analysis of the filter-wheel-closed data and only the normalizations of the instrumental background components were left free during the fit.…”

Mitigating the effects of particle background on the Athena Wide Field Imager

“…17 The similarity of the Case B and C fractions is remarkable, however, and we conclude that the Geant4 simulations produce a valid representation of the expected WFI background for our purposes of exploring correlations between particles tracks and valid events. 6 It is seen in both unclipped and clipped spectra.…”

“…To aid our analysis of the correlations between particle tracks and valid events, we assigned frames to "cases" in the same way as the XMM-Newton EPIC pn analysis, 6 namely: The spectrum over a wide energy band, showing pattern-based valid and invalid events separately. Valid events dominate by several orders of magnitude in the 2-7 keV band, while invalid events dominate above 100 keV, well outside the WFI sensitive band.…”

Reducing the Athena WFI charged particle background: results from Geant4 simulations

“…That valid events are spatially correlated with primary or secondary particle tracks from the same interacting cosmic ray was recognized early on in Geant4 simulations by the WFI Background Working Group 4 and in the analysis of in-orbit Chandra, Swift, and XMM-Newton data. [8][9][10] This correlation can be exploited by masking around particle tracks and flagging valid events within a certain distance; such events can later be filtered in ground processing depending on the science goals of the observation. However, this masking also reduces the signal and thus the efficiency of the instrument.…”