How Luminous Was the Galactic Supermassive Black Hole in the Past?

Frederick Baganoff (MIT Kavli Institute) , M. P. Muno (Caltech), W. N. Brandt (Penn State), S. Park (Penn State), and M. R. Morris (UCLA)

Repeated deep Chandra monitoring of Sgr A* over the past few years has revealed rapidly variable Fe fluorescence features within 6' (14 pc) of the supermassive black hole, suggesting that its X-ray luminosity may have been greater than 10^38 erg/s for at least 2-3 years about 60 years ago, before the first X-ray satellites were launched. These results will be discussed in the context of Chandra observations of Fe fluorescence in Sgr B2 and Sgr C, and arguments will be presented against the alternative hypotheses of irradiation by local X-ray binaries or excitation by low-energy cosmic ray electrons.