Exospheric neutral density near the Earth’s subsolar magnetopause deduced from the XMM-Newton X-ray observations during solar maximum
Résumé
Soft X-ray imaging telescopes on board the upcoming LEXI and SMILE missions provide an innovative way to visualize the Earth’s dayside magnetospheric system and its interaction with the solar wind through magnetic reconnection. Soft X-rays can be emitted when highly charged solar wind ions like O7+/O8+ catch electrons from neutral hydrogens, which is called solar wind charge exchange (SWCX). Magnetosheath and polar cusps emit strong soft X-rays because both solar wind ions and exospheric hydrogens are more densely populated than the surrounding areas. Exospheric neutral density near the subsolar magnetopause is an important parameter to predict SWCX signals and support the planning and data analysis of LEXI and SMILE. This presentation estimates exospheric neutral hydrogen density at 10 Earth radii subsolar location during solar maximum, using the X-ray Multi-Mirror (XMM) observations and the Open Geospace General Circulation Model (OpenGGCM) global magnetohydrodynamics (MHD) model. Image of XMM astrophysical satellite has SWCX component when the line of sight of the telescope passes through the dayside magnetosheath. We first select five XMM events during solar maximum and extract near-Earth SWCX signal after careful removal of all the other background components from the raw XMM X-ray data. Then, we conduct the OpenGGCM simulation of the five events obtained magnetosheath parameters required for the SWCX emission rate calculation. After validating the model results with the in-situ magnetosheath measurements or pre-existing magnetosheath models, we estimated the exospheric neutral density that gives the best match between the modeled and observed SWCX emissions. The estimated density during solar maximum is 42.5 – 65.1 cm-3, comparable to the previous XMM studies including Connor & Carter [2019] and Jung et al. [2022].