A high charge state coronal mass ejection seen through solar wind charge exchange emission as detected by XMM-Newton

We present the analysis of an observation by XMM–Newton that exhibits strongly variable, low-energy diffuse X-ray line emission. We reason that this emission is due to localized solar wind charge exchange (SWCX), originating from a passing cloud of plasma associated with a Coronal mass ejection (CME) interacting with neutrals in the Earth's exosphere. This case of SWCX exhibits a much richer emission-line spectrum in comparison with previous examples of geocoronal SWCX or in interplanetary space. We show that emission from O viii is very prominent in the SWCX spectrum. The observed flux from oxygen ions of Graphic is consistent with SWCX resulting from a passing CME. Highly ionized silicon is also observed in the spectrum, and the presence of highly charged iron is an additional spectral indicator that we are observing emission from a CME. We argue that this is the same event detected by the solar wind monitors Advanced Composition Explorer and Wind which measured an intense increase in the solar wind flux due to a CME that had been released from the Sun 2 d previous to the XMM–Newton observation.