Towards precision particle background estimation for future x-ray missions: correlated variability between Chandra ACIS and AMS

Abstract

A science goal of many future x-ray observatories is mapping the cosmic web through deep exposures of faint diffuse sources. Such observations require low background and the best possible knowledge of the remaining unrejected background. The dominant contribution to the background above 1-2 keV is from Galactic cosmic ray protons. Their flux and spectrum are modulated by the solar cycle but also by solar activity on shorter timescales. Understanding this variability may prove crucial to reducing background uncertainty for ESA’s Athena x-ray observatory and other missions with large collecting area. We examine the variability of the particle background as measured by ACIS on the Chandra x-ray observatory and compare that variability to that measured by the alpha magnetic spectrometer (AMS), a precision particle detector on the ISS. We show that cosmic ray proton variability measured by AMS is well matched to the ACIS background and can be used to estimate proton energies responsible for the background. We discuss how this can inform future missions.