Origin of the Galactic Diffuse X-ray Emission: Iron K-shell Line Diagnostics

TL;DR

This study analyzes iron and nickel K-shell line profiles in various Galactic X-ray emissions to understand their origins, revealing that some emissions are explained by known sources while others indicate additional high-temperature plasma components.

Contribution

It provides detailed spectral analysis of iron and nickel lines in Galactic X-ray emissions, identifying the need for additional components beyond known source populations.

Findings

GBXE spectrum is explained by mCVs, non-mCVs, and ABs.

GRXE shows excesses at iron line energies, indicating additional components.

GCXE has larger excesses linked to high-energy activity near the CMZ.

Abstract

This paper reports detailed K-shell line profiles of iron (Fe) and nickel (Ni) of the Galactic Center X-ray Emission (GCXE), Galactic Bulge X-ray Emission (GBXE), Galactic Ridge X-ray Emission (GRXE), magnetic Cataclysmic Variables (mCVs), non-magnetic Cataclysmic Variables (non-mCVs), and coronally Active Binaries (ABs). For the study of the origin of the GCXE, GBXE, and GRXE, the spectral analysis is focused on equivalent widths of the Fe K$\alpha$, Fe He$\alpha$, and Fe Ly$\alpha$ lines. The global spectrum of the GBXE is reproduced by a combination of the mCVs, non-mCVs, and ABs spectra. On the other hand, the GRXE spectrum shows significant data excesses at the Fe K$\alpha$ and Fe He$\alpha$ line energies. This means that additional components other than mCVs, non-mCVs, and ABs are required, which have symbiotic phenomena of cold gas and very high-temperature plasma. The GCXE spectrum shows larger excesses than those found in the GRXE spectrum at all the K-shell lines of iron and nickel. Among them the largest ones are the Fe K$\alpha$, Fe He$\alpha$, Fe Ly$\alpha$, and Fe Ly$\beta$ lines. Together with the fact that the scale heights of the Fe K$\alpha$, Fe He$\alpha$, and Fe Ly$\alpha$ lines are similar to that of the central molecular zone (CMZ), the excess components would be related to high-energy activity in the extreme envelopment of the CMZ.