Solar Wind Charge Exchange Soft X-Ray Emissions in the Magnetosphere during an Interplanetary Coronal Mass Ejection Compared to Its Driven Sheath

Soft X-ray emissions from solar wind charge exchange (SWCX) are applied in a recently developed approach to study the magnetosphere using panoramic soft X-ray imaging. This study represents the first attempt to distinguish magnetospheric SWCX emissions observed by XMM-Newton during the impact of an interplanetary coronal mass ejection (ICME) and its driven sheath on Earth. In addition, data from the Advanced Composition Explorer (ACE) were available during this same observational period, which is rare in previous studies. Results showed that SWCX emissions peaked during the ICME at approximately 2.3 times the mean of the observation period, although the solar wind flux decreased to a much lower level. A comparison of spectral results with ion data probed by ACE revealed that high ionization states in the ICME effectively enhanced line emission intensity for heavy ions (e.g., Ne, Mg, and Al). Thus, despite a low proton flux, elevated high-valence ion abundance in the ICME favors magnetospheric soft X-ray observations. Furthermore, the fitted X-ray flux of ion line emissions was consistent with elemental abundance ratios determined in situ by ACE, particularly for C⁵⁺, C⁶⁺, Ne⁹⁺, Mg¹¹⁺, and Mg¹²⁺. This confirms the viability of spectral diagnosis of SWCX emissions as a new method for remotely analyzing high-state ion distributions in solar wind. A time-correlated or two-stage efficiency factor is further suggested to better estimate X-ray intensity during an ICME impact, which was ~1.7 times higher in the ICME than in the sheath.