Empirical determination of extreme ultraviolet imager background

Abstract

We present an empirical determination of background levels of 30.4 nm extreme ultraviolet (EUV) radiation. A survey of 6 months of data from the IMAGE EUV imager indicates a relatively low quiescent background level. The most probable quiescent background count rate is 2.7 per pixel, per 600 s EUV image, equivalent to a brightness of approximately 27 mR. This quiescent background rate is approximate to 10 times larger than the detector dark rate, indicating that quiescent background levels are dominated by external light sources or penetrating particles. We hypothesize two light sources of quiescent background in the interplanetary or interstellar medium. The first is 30.4 nm light from nonplasmaspheric He+. The second is 58.4 nm light (from neutral He) that gets past the filter/mirror. The IMAGE EUV data also exhibit episodic, factor of 3-to-30 increases above the quiescent background rate, throughout the 6 month data set considered herein. Comparison of these elevated background levels with solar EUV and solar wind parameters indicates several contributing causes during active periods, including solar wind energetic (50 keV to 5 MeV) particles, solar wind density/pressure, and solar 30.4 nm flux. Plain LanguageSummary In this paper we study how much background noise is found in images from the Extreme Ultraviolet (or EUV) imager. This imager flew on a NASA mission called IMAGE from 2000 to 2005. Determination of the EUV background level lets researchers make the most of the archival data set and also helps plan future missions with improved EUV imagers.