O i fluorescent line contamination in soft X-ray diffuse background obtained with Suzaku/XIS

Abstract

Abstract The quantitative measurement of O VII line intensity is a powerful method for understanding the soft X-ray diffuse background. By systematically analyzing the O VII line intensity in 145 high-latitude Suzaku/XIS observations, the flux of O I fluorescent line in the XIS spectrum, contaminating the O VII line, is found to have an increasing trend with time especially after 2011. For these observations, the O VII line intensity would be overestimated unless taking into consideration the O I fluorescent line contamination. Since the O I line emission originates from solar X-rays, this increase suggests that the flux of incident solar X-rays at the O I fluorescence energy tend to be larger than that in the early phase of Suzaku observations (2005–2010).