Unveiling the origin of XMM-Newton soft proton flares II. Systematics in the proton spectral analysis

TL;DR

This study analyzes soft proton flares in XMM-Newton data, revealing that proton spectra are best modeled by a power law with an additional component to account for matrix generation imprecision, influenced by seasonal and solar activity variations.

Contribution

It introduces a systematic analysis of proton spectral matrices using real data, highlighting the need for a second component in the spectral model.

Findings

Proton spectra are well described by a power law.

A second phenomenological component improves spectral fits.

Seasonal and solar activity effects influence the proton environment.

Abstract

Low-energy protons entering the field of view of the XMM-Newton telescope scatter with the X-ray mirror surface and might reach the X-ray detectors on the focal plane. They manifest in the form of a sudden increase in the rates, usually referred to as soft proton flares. By knowing the conversion factor between the soft proton energy and the deposited charge on the detector, it is possible to derive the incoming flux and to study the environment of the Earth magnetosphere at different distances. We present the results of testing these matrices with real data for the first time, while also exploring the seasonal and solar activity effect on the proton environment. The selected spectra are relative to 55 simultaneous MOS and PN observations with flares raised in four different temporal windows: December-January and July-August of 2001-2002 (solar maximum) and 2019-2020 (solar minimum). The main result of the spectral analysis is that the physical model representative of the proton spectra at the input of the telescope is a power law. However, a second and phenomenological component is necessary to take into account imprecision in the generation of the matrices at softer energies.