Spatial and Temporal Variations of the Diffuse Iron 6.4 keV Line in the   Galactic Center Region
  We analyze the diffuse Fe I K-alpha line generated in the diffuse interstellar molecular hydrogen by primary photons or subrelativistic protons injected by Sagittarius (Sgr) A*. We showed that unlike emission from compact molecular clouds, this emission can be permanently observed in the directions of the Galactic center. We conclude that the diffuse emission of 6.4 keV line observed at present is probably due to Fe I K-alpha vacancy production by primary photons if the X-ray luminosity of Sgr A* was about Lx ~ 10^39-10^40 erg/s. In principle these data can also be described in the framework of the model when the 6.4 keV line emission is generated by subrelativistic protons generated by accretion onto the central black hole but in this case extreme parameters of this model are necessary. 
D. O. Chernyshov, V. A. Dogiel, M. Nobukawa, T. G. Tsuru, K. Koyama,   H. Uchiyama, H. Matsumoto
astro-ph.GA