The XMM-Newton Line Emission Analysis Program (X-LEAP) III: Earth's Magnetospheric X-ray Emission Revealed by 22-Year XMM-Newton Observations

The magnetosphere, protecting the Earth from intense solar activity, is also shaped by the solar wind, while its structure is still uncertain in observation. In this study, we map the X-ray emission in the magnetosphere, which is induced by the charge exchange between the highly-ionized solar wind and the neutral gas around the Earth, known as the magnetospheric solar wind charge exchange (SWCX). In particular, we extract the magnetospheric SWCX in the O VII line emission data adopted from the XMM Line Emission Analysis Program (X-LEAP). The observed magnetospheric SWCX shows an enhanced emission of approximately I OVII mag about 2 photons cm-2 s-1 sr-1 toward the Sun, showing a consistent shape predicted by numerical simulations. Furthermore, this magnetospheric SWCX exhibits a dependence on the XMM pointing direction, which traces the path length of SWCX emission in the Earth's magnetosphere. Building on this directional dependence, we model the 3D magnetosheath structure using soft X-ray observations for the first time, constraining the averaged boundary geometry and SWCX emissivity distribution over 22 years. Finally, utilizing the XMM data, we derive an empirical O VII emission efficiency of alpha OVII=(2.1 plus or minus0.4) times 10-16 eV,cm squared.