Discovery of K-Shell Emission Lines of Neutral Atoms in the Galactic Center Region

The K-shell emission line of neutral iron from the Galactic center (GC) region is one of the keys concerning the structure and activity of the GC. The origin is still an open question, but possibly due either to X-ray radiation or to electron bombarding to neutral atoms. To address this issue, we analyzed the Suzaku X-ray spectrum from the GC region of intense neutral iron line emission, and report on the discovery of K$\alpha$ lines of neutral argon, calcium, chrome, and manganese atoms. The equivalent widths of these K$\alpha$ lines indicate that the metal abundances in the GC region should be $\sim $1.6 and $\sim $4 of the solar value, depending on the X-ray and electron origins, respectively. On the other hand, the metal abundances in the hot plasma in the GC region are found to be $\sim $1–2 solar. These results favor that the origin of the neutral K$\alpha$ lines is due to X-ray irradiation