Two methods for separating the magnetospheric solar wind charge exchange soft X-ray emission from the diffuse X-ray background

Abstract

Solar wind charge exchange (SWCX) is the process of solar wind high-valence ions exchanging charges with neutral components and generating soft X-rays. Recently, detecting the SWCX emission from the magnetosphere is proposed as a new technique to study the magnetosphere using panoramic soft X-ray imaging. To better prepare for the data analysis of upcoming magnetospheric soft X-ray imaging missions, this paper compares the magnetospheric SWCX emission obtained by two methods in an XMM-Newton observation, during which the solar wind changed dramatically. The two methods differ in the data used to fit the diffuse X-ray background (DXB) parameters in spectral analysis. The method adding data from the ROSAT All-Sky Survey (RASS) is called the RASS method. The method using the quiet observation data is called the Quiet method, where quiet observations usually refer to observations made by the same satellite with the same target but under weaker solar wind conditions. Results show that the spectral compositions of magnetospheric SWCX emission obtained by the two methods are very similar, and the changes in intensity over time are highly consistent, although the intensity obtained by the RASS method is about \begin{document}$2.68\,\pm\, 0.56$\end{document} keV \begin{document}${\rm{cm}}^{-2} {\rm{s}}^{-1} {\rm{sr}}^{-1}$\end{document} higher than that obtained by the Quiet method. Since the DXB intensity obtained by the RASS method is about \begin{document}$2.84\,\pm\, 0.74$\end{document} keV \begin{document}${\rm{ cm}}^{-2} {\rm{s}}^{-1} {\rm{sr}}^{-1}$\end{document} lower than that obtained by the Quiet method, and the linear correlation coefficient between the difference of SWCX and DXB obtained by the two methods in different energy band is close to −1, the differences in magnetospheric SWCX can be fully attributed to the differences in the fitted DXB. The difference between the two methods is most significant when the energy is less than 0.7 keV, which is also the main energy band of SWCX emission. In addition, the difference between the two methods is not related to the SWCX intensity and, to some extent, to solar wind conditions, because SWCX intensity typically varies with the solar wind. In summary, both methods are robust and reliable, and should be considered based on the best available options.

Keywords

• solar wind charge exchange (swcx)
• rosat all-sky survey (rass)
• soft x-ray
• x-ray imaging
• magnetosphere