X-ray Iron Line Emission From Sagittarius A*

The line features between [6, 7] keV contain the critical information about the physical origin of the steady X-ray emission from Sagittarius A* and its vicinity. The observations by Baganoff et al. (2003) show that the line center detected outside of Bondi radius is about 6.5(-0.2)(+0.1) keV, which indicates that the iron ions are not in a collisional ionization equilibrium (CIE). Indeed current models assume CIE and hence predict that iron ions are dominated by H and He-like ions with the line center being close to 6.7 keV. New spectral data from about 1 Ms of Chandra ACIS observations allow us to better constrain iron line features, which offers a good indicator to discriminate different models. We aim to examine non-equilibrium ionization (NET) effects for Sgr A* and its vicinity using the various dynamic models based on the NET code by Ji et al. (2006). Our preliminary results for the vicinity of Sgr A* show that the center of Fe ion features is 6.48(-0.02)(+0.01) keV and sigma = 87.2(-1.7)(+1.5) eV.