XRISM Collaboration paper on the supernova remnant Sgr A East

Our XRISM paper on the supernova remnant Sagittarius A East (Sgr A East) has been accepted for publication in PASJ as a Letter (ADS). Sgr A East is a remnant located in a unique environment, the immediate vicinity (< a few pc) of the supermassive black hole of our Galaxy, Sgr A*. We are interested in the remnant evolution in such a peculiar environment. Our spectroscopy of the Fe-K emission using XRISM clearly showed that the Fe plasma is in an “over-ionized” state, as the emission exhibits an enhanced Fe Hea forbidden/resonance ratio and Fe-K lines from a broad range of charge states (H-, He-, Li-, and Be-like). The over-ionization requires some peculiar evolutionary paths. In our case, we conclude that a quick thermalization in dense circumstellar material and subsequent expansion into low-density interstellar medium, or intense photoionization by the black hole Sgr A* may have triggered the over-ionization. Further investigation will certainly be fascinating!