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Variability of the unrejected particle background on Chandra ACIS

Presentation #108.10 in the session “Missions and Instruments (Poster)”.

Published onApr 01, 2022
Variability of the unrejected particle background on Chandra ACIS

A science goal of many future X-ray observatories is mapping the cosmic web through deep exposures of faint diffuse sources, such as clusters and groups of galaxies and the intergalactic medium. Such observations require low background and the best possible knowledge of the remaining unrejected background. For most detectors and orbits, the dominant contribution to the unrejected background above 1-2 keV is from Galactic Cosmic Ray (GCR) protons. The flux and spectrum of these protons are modulated by the 11-year solar cycle but also with solar activity on much shorter timescales of months, weeks, or even days. Understanding this variability may prove crucial to reducing background uncertainty to the level required by ESA’s Athena X-ray Observatory and other future large collecting area missions.

We will examine of the variability of the particle background as measured by the Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray Observatory, and then compare that variability to measurements by the Alpha Magnetic Spectrometer (AMS), a precision particle physics detector on the International Space Station. We will show that the cosmic ray proton variability measured by AMS is very well matched to the ACIS variability and can be used to estimate the proton energies responsible for the ACIS unrejected background. We will discuss how this knowledge can inform future missions, by inclusion of special purpose particle monitors, as is under investigation for Athena, or by comparison to other space-based particle monitors.

This work was done as part of the Athena WFI Background Working Group, a consortium including MPE, INAF/IASF-Milano, IAAT, Open University, MIT, SAO, and Stanford. We gratefully acknowledge support from NASA grant NNX17AB07G.


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