Evidence for solar-wind charge-exchange X-ray emission from the earth's magnetosheath

Abstract

We report an apparent detection of the C VI 4p to Is transition line at 459 eV, during a long-term enhancement (LTE) in the Suzaku north ecliptic pole observation of 2005 September 2. The observed line intensity is comparable to that of the C VI 2p to Is line at 367 eV. This is strong evidence for the charge-exchange process. In addition, O VII, O VIII, Ne X, and Mg XI lines showed clear enhancements. There are also features in the 750-900 eV range that could be due to some combination of Fe L lines, higher order transitions of O vin (3p to 1s and 6p to 1 s), and a Ne IX line. From the correlation of the X-ray intensity with the solar-wind flux on time scales of about half a day, and from the short-term (∼ 10 minutes) variations of the X-ray intensity, these lines most likely arise from solar-wind heavy ions interacting with neutral material in the Earth's magnetosheath. A hard power-law component is also necessary to explain the LTE spectrum. Its origin is not yet known. Our results indicate that solar activity can significantly contaminate Suzaku cosmic X-ray spectra below ∼ 1 keV. Recommendations are provided for recognizing such contamination in observations of extended sources. © 2007. Astronomical Society of Japan.