2023RAA....23h5005N

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 (∼2″-20″, ∼0.08-0.8 pc) X-ray emission around Sgr A*. Over two-decade 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″-18″ region, ${\epsilon }_{{\rm{c}}}={6.65}_{-0.03}^{+0.02}\,\mathrm{keV}$, is comparable to that (${\epsilon }_{{\rm{c}}}={6.60}_{-0.03}^{+0.05}\,\mathrm{keV}$) of the inner 2″-5″ region. This is somewhat unexpected, since the gas temperature decreases further away from the 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 ∼8″-10″ remain in a CIE state, outside of this radius they will be in the NEI state. A comparison of the properties of ∼6.6 keV iron lines between CIE and NEI is addressed. Interestingly, the NEI interpretation of outer region is supported by the Chandra line center ϵ_c measurements of this region.