Resolving the Fe K$α$ Doublet of the Galactic Center Molecular Cloud G0.11-0.11 with XRISM
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| Format: | Preprint |
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2026
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| _version_ | 1866912804098801664 |
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| author | DiKerby, Stephen Zhang, Shuo Nobukawa, Kumiko Nobukawa, Masayoshi Aoki, Yuma Uteg, Jack |
| author_facet | DiKerby, Stephen Zhang, Shuo Nobukawa, Kumiko Nobukawa, Masayoshi Aoki, Yuma Uteg, Jack |
| contents | Fe K$α$ line emission from Galactic center molecular clouds can be produced either via fluorescence after illumination by an X-ray source or by cosmic ray ionization. Unparalleled high-resolution X-ray spectroscopy obtained by XRISM-Resolve for the galactic center molecular cloud G0.11-0.11 resolves its Fe K$α$ line complex for the first time, and points to a new method for discrimination between the X-ray reflection and cosmic ray ionization models. The Fe K$α$ line complex is resolved into Fe K$α_1$ at $E_{1} = 6.4040 \: \rm{keV}$ and Fe K$α_2$ at $E_{2}= 6.3910 \:\rm{keV}$. Both lines have non-instrumental FWHM of $\approx 3 \:\rm{eV}$, close to the predicted quantum mechanical width of the lines, suggesting scant other sources of line broadening other than instrumental and quantum effects. We measure a radial velocity of $v_{\rm{LSR}} = 50 \pm 12_{fit} \pm 14_{scale} \:\rm{km/s}$ for G0.11-0.11, achieving the same precision reached by radio observations of such clouds. The high-resolution spectrum tests for the presence of secondary Fe K$α$ lines, expected as a signature of cosmic ray proton/ion ionization. The absence of the secondary lines argues against the cosmic ray ionization model for G0.11-0.11. In the preferred X-ray reflection model, if the illuminating source is Sgr A$^{\star}$, the required luminosity for an X-ray outburst about 200 years ago is $L_8 \approx 10^{38} \:\rm{erg/s}$ in an $8\:\rm{keV}$-wide band at $8\:\rm{keV}$. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2601_02482 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Resolving the Fe K$α$ Doublet of the Galactic Center Molecular Cloud G0.11-0.11 with XRISM DiKerby, Stephen Zhang, Shuo Nobukawa, Kumiko Nobukawa, Masayoshi Aoki, Yuma Uteg, Jack High Energy Astrophysical Phenomena Instrumentation and Methods for Astrophysics Fe K$α$ line emission from Galactic center molecular clouds can be produced either via fluorescence after illumination by an X-ray source or by cosmic ray ionization. Unparalleled high-resolution X-ray spectroscopy obtained by XRISM-Resolve for the galactic center molecular cloud G0.11-0.11 resolves its Fe K$α$ line complex for the first time, and points to a new method for discrimination between the X-ray reflection and cosmic ray ionization models. The Fe K$α$ line complex is resolved into Fe K$α_1$ at $E_{1} = 6.4040 \: \rm{keV}$ and Fe K$α_2$ at $E_{2}= 6.3910 \:\rm{keV}$. Both lines have non-instrumental FWHM of $\approx 3 \:\rm{eV}$, close to the predicted quantum mechanical width of the lines, suggesting scant other sources of line broadening other than instrumental and quantum effects. We measure a radial velocity of $v_{\rm{LSR}} = 50 \pm 12_{fit} \pm 14_{scale} \:\rm{km/s}$ for G0.11-0.11, achieving the same precision reached by radio observations of such clouds. The high-resolution spectrum tests for the presence of secondary Fe K$α$ lines, expected as a signature of cosmic ray proton/ion ionization. The absence of the secondary lines argues against the cosmic ray ionization model for G0.11-0.11. In the preferred X-ray reflection model, if the illuminating source is Sgr A$^{\star}$, the required luminosity for an X-ray outburst about 200 years ago is $L_8 \approx 10^{38} \:\rm{erg/s}$ in an $8\:\rm{keV}$-wide band at $8\:\rm{keV}$. |
| title | Resolving the Fe K$α$ Doublet of the Galactic Center Molecular Cloud G0.11-0.11 with XRISM |
| topic | High Energy Astrophysical Phenomena Instrumentation and Methods for Astrophysics |
| url | https://arxiv.org/abs/2601.02482 |