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

TL;DR

This paper reports the discovery of neutral argon, calcium, chrome, and manganese K-alpha emission lines in the Galactic center, suggesting X-ray irradiation as their origin and providing insights into the region's metal abundances.

Contribution

First detection of multiple neutral atom K-alpha lines in the Galactic center, supporting X-ray irradiation as the origin and estimating metal abundances.

Findings

Neutral K-alpha lines of Ar, Ca, Cr, Mn detected

Metal abundances in GC region are ~1.6-4 times solar

Results favor X-ray irradiation as the origin

Abstract

The K-shell emission line of neutral irons from the Galactic center (GC) region is one of the key for the structure and activity of the GC. The origin is still 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 Kalpha lines of neutral argon, calcium, chrome, and manganese atoms. The equivalent widths of these Kalpha lines indicate that the metal abundances in the GC region should be ~1.6 and ~4 of solar value, depending on the X-ray and the electron origins, respectively. On the other hand, the metal abundances in the hot plasma in the GC region are found to be ~1-2 solar. These results favor that the origin of the neutral Kalpha lines are due to X-ray irradiation.