Correlated Sub-mm and X-ray Variability in Sgr A*

Abstract

PAPER WITHDRAWN. The recent detection of Sgr A* in the X-ray band, together with the radio polarization measurements conducted over the past few years, offer the best constraints yet for understanding the nature of the emitting gas within several Schwarzschild radii ($r_S$) of this supermassive black hole candidate at the Galactic Center. Earlier, we showed that the sub-mm radiation from this source may be associated with thermal synchrotron emission from an inner Keplerian region within the circularization radius of the accreting plasma. In this paper, we extend this analysis in a very important way, by calculating the implied high-energy emission of Sgr A* associated with the orbiting, hot, magnetized gas. We find that for the accretion rate inferred from the fits to the sub-mm data, the dominant contribution to Sgr A*'s X-ray flux is due to self-Comptonization of the radio photons, rather than from bremsstrahlung. The latter is a two-body process, which would produce significant X-ray emission only at much higher accretion rates. This picture leads to the testable prediction that the physical conditions within the inner $\sim5r_S$ are variable on a time scale of order a year. In particular, the accretion rate $\dot M$ appears to have changed by about 15% between the sub-mm measurements in 1996 and 1999. Given that the radio and self-Comptonized fluxes are strongly correlated in this picture, the upcoming second generation Chandra observations of Sgr A* may provide the direct evidence required to test this model.