Origin and Composition of the Galactic Diffuse X-Ray Emission Spectra by Unresolved X-Ray Sources

Katsuji Koyama; Masayoshi Nobukawa

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arXiv · 2401.09726

Origin and Composition of the Galactic Diffuse X-Ray Emission Spectra by Unresolved X-Ray Sources

Katsuji Koyama·Masayoshi Nobukawa

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Abstract

The Galactic diffuse X-ray emission (GDXE) can be spatially segmented 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 expressed by the assembly of compact X-ray sources, which are either the white dwarfs (WDs), or the X-ray active stars, consisting of binaries with late type stars. The WDs have either strong magnetic field (mCV), or weak magnetic field (non-mCV). The WDs and X-ray active stars are collectively called as compact X-ray stars. However, spectral fittings by the assembly of all compact X-ray stars for the GCXE, GRXE, and GBXE are rejected leaving significant excess near the energies of K$\alpha$, He$\alpha$, Ly$\alpha$ lines. These excesses are found in the collisional ionization equilibrium (CIE) plasma. Thus the spectra of the GRXE and GBXE are improved by adding CIE-SNRs. However the GCXE spectrum is still unacceptable with significant data excess due to the radiative recombination emission (RP-plasma). Then the GCXE fit is significantly improved by adding aged RP-SNRs. The aged RP-SNRs would be made by a past big flare of Sgr~A$^*$ emitting either hard X-rays or low-energy cosmic-rays. The big flares may excite Fe and Ni atoms in cold diffuse gas (CM), and emit fluorescent X-ray lines. The CIE-SNRs, RP-SNRs and CM are called as diffuse X-ray sources. This paper presents the spectral fits by the assembly of all the compact and diffuse X-ray sources together with high quality spectra and combined fit among all GDXE of GCXE, GRXE, and GBXE. This provides the first scenario to quantitatively and comprehensively predict the origin of the GDXE spectra.

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Katsuji Koyama, Masayoshi Nobukawa. 2024-01-18. Origin and Composition of the Galactic Diffuse X-Ray Emission Spectra by Unresolved X-Ray Sources. https://arxiv.org/abs/2401.09726

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