Measurement of L-Shell Emission from Iron-Group Elements for High-Resolution X-Ray Spectroscopy in Future Astronomy

Abstract

Measuring abundance of iron-group elements (IGEs; Cr, Mn, Fe, and Ni) is essential for understanding astrophysical phenomena such as supernovae. The L-shell emissions from IGEs will soon be resolved by next-generation X-ray satellites, enabling more accurate measurements of abundance. However, theoretical calculations for these L-shell transitions have not been sufficiently validated using experimental work. Herein, large helical device (LHD) experiments that measured L-shell emission from Ni and Mn are reported. The temporal evolution of LHD plasma is characterized by three phases, each of which resolves different L-shell emissions. We modeled EUV-Short spectra considering LHD plasma structure with AtomDB, an atomic database widely used in the X-ray astronomy community. We discovered that the observed intensity ratios of the 3C (2p⁵3d^{1 1}P₁ → 2p^{6 1}S₀) to 3D (2p⁵3d^{1 3}D₁ → 2p^{6 1}S₀) transition of Ne-like ions are 0.4 - 0.6 times lower than the theoretically predicted ratios.