Kavli Affiliate: Marshall W. Bautz
| First 5 Authors: Gerrit Schellenberger, Ralph Kraft, Paul Nulsen, Eric D. Miller, Marshall W. Bautz
| Summary:
The level and uncertainty of the particle induced background in CCD detectors
plays a crucial role for future X-ray instruments, such as the Wide Field
Imager (WFI) onboard Athena. To mitigate the background systematic
uncertainties, which will limit the Athena science goals, we aim to understand
the relationship between the energetic charged particles interacting in the
detector and satellite, and the instrumental science background to an
unprecedented level. These particles produce easily identified "cosmic-ray
tracks" along with less easily identified signals produced by secondary
particles, e.g., X-rays generated by particle interactions with the instrument
and indistinguishable from genuine sky X-rays. We utilize the Small Window Mode
of the PN camera onboard XMM-Newton to understand the time, spatial and energy
dependence of the various background components, particularly the particle
induced background. While the distribution of particle events follows expected
detector readout patterns, we find a particle track length distribution
inconsistent with the simple, isotropic model. We also find that the detector
mode-specific readout results in a shifted Cu fluorescent line. We illustrate
that on long timescales the variability of the particle background correlates
well with the solar cycle. This 20-year lightcurve, can be reproduced by a
particle detector onboard Chandra, the HRC anti-coincidence shield. We conclude
that the self-anti-coincidence method of removing X-ray-like events near
detected particle tracks in the same frame can be optimized with the inclusion
of additional information, such as the energy of the X-ray. The results
presented here are relevant for any future pixelated X-ray imaging detector,
and could allow the WFI to probe to truly faint X-ray surface brightness.
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