LAUSR

The feeding and feedback processes at the vicinity of a supermassive black hole (BH) are essential for our understanding of the connection between supermassive BH and its host galaxy. In this work, we provide a detailed investigation, both observational and theoretical, on the diffuse ($\sim 2\arcsec - 20\arcsec$ $\sim0.08-0.8$ pc) X-ray emission around Sgr A*. Over two-decade {\it Chandra} observations are gathered to obtain highest signal-to-noise to date. We find that, the line center of iron lines of the outer $8\arcsec\ - 18\arcsec$ region, $\epsilon_{\rm c}=6.65_{-0.03}^{+0.02}\,{\rm keV}$, is comparable to that ($\epsilon_{\rm c}=6.60_{-0.03}^{+0.05}\,{\rm keV}$) of the inner $2\arcsec\ - 5\arcsec$ region. This is somewhat unexpected, since the gas temperature decreases further away from central BH. Based on a dynamical inflow-outflow model that considers the gas feeding by stellar winds from Wolf-Rayet stars, we calculate the X-ray spectrum based on both the conventional collisional ionization equilibrium (CIE) assumption, and the newly developed non-equilibrium ionization (NEI) assumption. We find that, theoretically gases within $\sim 8\arcsec\ - 10\arcsec$ remain in a CIE state, outside of this radius they will be in the NEI state. A comparison of the properties of $\sim 6.6\,{\rm keV}$ iron lines between CIE and NEI is addressed. Interestingly, the NEI interpretation of outer region is supported by the \chandra\ line center $\epsilon_{\rm c}$ measurements of this region.