Overionized plasma in the supernova remnant Sagittarius A East anchored by XRISM observations
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866917868175622144 |
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| author | XRISM Collaboration |
| author_facet | XRISM Collaboration |
| contents | Sagittarius A East is a supernova remnant with a unique surrounding environment, as it is located in the immediate vicinity of the supermassive black hole at the Galactic center, Sagittarius A*. The X-ray emission of the remnant is suspected to show features of overionized plasma, which would require peculiar evolutionary paths. We report on the first observation of Sagittarius A East with X-Ray Imaging and Spectroscopy Mission (XRISM). Equipped with a combination of high-resolution microcalorimeter spectrometer and large field-of-view CCD imager, we for the first time resolved the Fe XXV K-shell lines into fine structure lines and measured the forbidden-to-resonance intensity ratio to be $1.39\pm0.12$, which strongly suggests the presence of overionized plasma. We obtained a reliable constraint on the ionization temperature just before the transition into the overionization state, to be > 4 keV. The recombination timescale was constrained to be < $8\times10^{11}$ cm$^{-3}$ s. The small velocity dispersion of $109\pm6$ km s$^{-1}$ indicates a low Fe ion temperature < 8 keV and a small expansion velocity < 200 km s$^{-1}$. The high initial ionization temperature and small recombination timescale suggest that either rapid cooling of the plasma via adiabatic expansion from dense circumstellar material or intense photoionization by Sagittarius A* in the past may have triggered the overionization. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2412_00676 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Overionized plasma in the supernova remnant Sagittarius A East anchored by XRISM observations XRISM Collaboration High Energy Astrophysical Phenomena Sagittarius A East is a supernova remnant with a unique surrounding environment, as it is located in the immediate vicinity of the supermassive black hole at the Galactic center, Sagittarius A*. The X-ray emission of the remnant is suspected to show features of overionized plasma, which would require peculiar evolutionary paths. We report on the first observation of Sagittarius A East with X-Ray Imaging and Spectroscopy Mission (XRISM). Equipped with a combination of high-resolution microcalorimeter spectrometer and large field-of-view CCD imager, we for the first time resolved the Fe XXV K-shell lines into fine structure lines and measured the forbidden-to-resonance intensity ratio to be $1.39\pm0.12$, which strongly suggests the presence of overionized plasma. We obtained a reliable constraint on the ionization temperature just before the transition into the overionization state, to be > 4 keV. The recombination timescale was constrained to be < $8\times10^{11}$ cm$^{-3}$ s. The small velocity dispersion of $109\pm6$ km s$^{-1}$ indicates a low Fe ion temperature < 8 keV and a small expansion velocity < 200 km s$^{-1}$. The high initial ionization temperature and small recombination timescale suggest that either rapid cooling of the plasma via adiabatic expansion from dense circumstellar material or intense photoionization by Sagittarius A* in the past may have triggered the overionization. |
| title | Overionized plasma in the supernova remnant Sagittarius A East anchored by XRISM observations |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2412.00676 |