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A. Broderick, R. D. Blandford (Caltech)
Recent observations of Sgr A* have detected an anomalously high degree of circular polarization (CP) at 4.8 and 8.4 MHz (e.g. Bower 2000). CXO observations imply that in the Galactic center the accretion rate onto the black hole is lower than previously suspected. These two observations suggest that it may be possible to observe emission from the ergosphere at mm wavelengths. In addition, in some disk-jet models the emitting region is no larger than a few horizon radii. This motivates an investigation of the propagation of waves in a magneto-active plasma residing in a curved space-time.
In the geometric optics limit, we have developed a formalism to handle the ray propagation of plasma modes under these circumstances.This includes a covariant propagation equation for the polarization. A radiative transfer equation is used to determine the intensity of the mode along a given ray. Some possible implications are suggested for Sgr A*.