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Paper: Diffuse X-Ray Sky in the Galactic Center
Volume: 528, New Horizons in Galactic Center Astronomy and Beyond
Page: 3
Authors: Koyama, K.
Abstract: The Galactic Diffuse X-ray Emission (GDXE) in the Milky Way Galaxy is spatially and spectrally decomposed into the Galactic Center X-ray Emission (GCXE), the Galactic Ridge X-ray Emission (GRXE) and the Galactic Bulge X-ray Emission (GBXE). The X-ray spectra of the GDXE are characterized by the strong K-shell lines of the highly ionized atoms, the brightest are the K-shell transition (principal quantum number n=2→1) of neutral iron (Fe I-Kα), He-like iron (Fe XXV-Heα) and He-like sulfur (S XV-Heα) lines. From these lines, the spectra of the GCXE, GBXE and GRXE are found to be different with each other. Thus the origins would be also different. Phenomenologically, the GCXE spectrum is decomposed into a Low Temperature Plasma (LTP), a High Temperature Plasma (HTP), and a Power Law (PL) component with Fe I-Kα. Remarkable emission lines in the HTP are Fe XXV-Heα and Fe XXVI-Lyα. From these line structures, we conclude that the major origin of HTP is not discrete sources (Cataclysmic Variable) but is high temperature (about 7 keV) diffuse plasma. The LTP is characterized by bright S XV-Heα and S XVI-Lyα lines.Then the major origin of LTP may not be discrete sources (AB: Active Binary star), but would be diffuse plasma of about 1 keV temperature. The scale heights and equivalent widths of the Fe I-Kα, Fe XXV-Heα and Fe XXVI-Lyα (H-like iron) lines are different among the GCXE, GBXE and GRXE. Thus from the point of SH, these components are in different origin. This paper overviews the research history and the present understandings of the GDXE, in particular focus on the origin of the HTP in the GCXE.
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