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

Presentation #108.12 in the session “Missions and Instruments (Poster)”.

Published onApr 01, 2022
Mitigating the effects of particle background on the Athena Wide-Field Imager

The Wide Field Imager (WFI) flying on Athena will usher in the next era of studying the hot and energetic Universe. Among Athena’s ambitious science programs are observations of faint, diffuse sources limited by statistical and systematic uncertainty in the background produced by high-energy cosmic ray particles. These particles produce easily identified “cosmic-ray tracks” along with less easily identified signals produced by secondary photons or X-rays generated by particle interactions with the instrument. We present results from a study of background-reduction techniques that exploit the spatial correlation between cosmic-ray particle tracks and secondary events, using Geant4 simulations to generate a realistic particle background signal and processing that signal to produce a realistic WFI observation containing only particle background. The technique under study, Self Anti-Coincidence or SAC, then selectively filters regions of the detector around particle tracks, turning the WFI into its own anti-coincidence detector. We show that SAC is effective at improving the systematic uncertainty for observations of faint, diffuse sources, but at the cost of statistical uncertainty due to a reduction in signal. If sufficient pixel pulse-height information is telemetered to the ground for each frame, then this technique can be applied selectively based on the science goals, providing flexibility without affecting the data quality for other science. The results presented here are relevant for any future silicon-based pixelated X-ray imaging detector, and could allow the WFI and similar instruments to probe to truly faint X-ray surface brightness. We gratefully acknowledge support for this work from NASA grant NNX17AB07G and from the UK Space Agency.

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