Review of the particle background of the Athena X-IFU instrument

TL;DR

This paper characterizes the particle-induced background of the Athena X-IFU instrument, comparing environments at L1 and L2, and assesses the instrument's ability to observe faint sources like galaxy cluster outskirts.

Contribution

It provides a detailed Monte Carlo simulation analysis of particle backgrounds at L1 and L2, and evaluates the impact on observing faint, diffuse X-ray sources.

Findings

GCR background levels meet mission requirements.

Soft Protons background is similar at L1 and L2, but L2 is less characterized.

Background levels hinder characterization of cluster outskirts without reduction.

Abstract

X-ray observations are limited by the background, due to intrinsic faintness or diffuse nature of the sources. The future Athena X-ray observatory has among its goals the characterization of these sources. We aim at characterizing the particle-induced background of the Athena microcalorimeter, in both its low (Soft Protons) and high (GCR) energy induced components, to assess the instrument capability to characterize background dominated sources such as the outskirts of clusters of galaxies. We compare two radiation environments, namely the L1 and L2 Lagrangian points, and derive indications against the latter. We estimate the particle-induced background level on the X-IFU microcalorimeter with Monte Carlo simulations, before and after all the solutions adopted to reduce its level. Concerning the GCR induced component the background level is compliant with the mission requirement. Regarding the Soft Protons component, the analysis does not predict dramatically different backgrounds in the L1 and L2 orbits. However, the lack of data concerning the L2 environment labels it as very weakly characterizable, and thus we advise against its choice as orbit for X-ray missions. We then use these background levels to simulate the observation of a typical galaxy cluster from its center out to 1.2 R200 to probe the characterization capabilities of the instrument out to the outskirts. We find that without any background reduction it is not possible to characterize the properties of the cluster in the outer regions. We also find no improvement of the observations when carried out during the solar maximum with respect to the solar minimum conditions.