Identifying XMM-Newton observations affected by solar wind charge exchange - Part II

TL;DR

This study analyzes over 3000 XMM-Newton observations to identify solar wind charge exchange effects, developing a method to estimate SWCX emission based on solar wind data and assessing its correlation with solar activity.

Contribution

The paper extends previous methods to detect SWCX in XMM-Newton data and introduces a new approach to estimate SWCX emission using solar wind parameters, covering a large dataset.

Findings

Approximately 3.4% of observations show SWCX effects.

SWCX is more common when observing through Earth's subsolar magnetosheath.

The emission estimation model predicts fluxes within a factor of a few in most cases.

Abstract

We wished to analyse a sample of observations from the XMM-Newton Science Archive to search for evidence of exospheric solar wind charge exchange (SWCX) emission. We analysed 3012 observations up to and including revolution 1773. The method employed extends from that of the previously published paper by these authors on this topic. We detect temporal variability in the diffuse X-ray background within a narrow low-energy band and contrast this to a continuum. The low-energy band was chosen to represent the key indicators of charge exchange emission and the continuum was expected to be free of SWCX. Approximately 3.4 % of observations studied are affected. We discuss our results with reference to the XMM-Newton mission. We further investigate remarkable cases by considering the state of the solar wind and the orientation of XMM-Newton at the time of these observations. We present a method to approximate the expected emission from observations, based on given solar wind parameters taken from an upstream solar wind monitor. We also compare the incidence of SWCX cases with solar activity. We present a comprehensive study of the majority of the suitable and publically available XMM-Newton Science Archive to date, with respect to the occurrence of SWCX enhancements. We present our SWCX-affected subset of this dataset. The mean exospheric-SWCX flux observed within this SWCX-affected subset was 15.4 keV cm-2 s-1 sr-1 in the energy band 0.25 to 2.5 keV. Exospheric SWCX is preferentially detected when XMM-Newton observes through the subsolar region of the Earth's magnetosheath. The model developed to estimate the expected emission returns fluxes within a factor of a few of the observed values in the majority of cases, with a mean value at 83 %.