ar X iv : a st ro - p h / 03 02 22 8 v 1 1 1 Fe b 20 03 Linear and Circular Polarization from Sagittarius A

We describe recent results for Sgr A*, M81* and other low luminosity active galactic nuclei. We have conducted linear and circular polarimetry over a frequency range of 1.4 to 230 GHz and detected a variety of phenomena. The polarization properties of the studied sources are substantially different from higher powered AGN. In the case of Sgr A*, we are able to eliminate ADAFs and Bondi-Hoyle flows as possible models based on mm λ polarimetry. Our success with Sgr A* demonstrates that we can learn about the nature of accretion and outflow in these sources with unprecedented detail. We may also develop probes of general relativity in the strong-field limit. We have engaged in a lengthy program exploring the linear and circular polarization properties of Sagittarius A* (Bower et al. 1999a, Bower, Falcke & Backer 1999b, Bower et al. 1999c, Bower et al. 2001, Bower et al. 2002a, Bower et al. 2003). We summarize some of the key results of that program here. 1.1. Circular << Linear at cm λ VLA observations between 1.4 and 15 GHz show that circular polarization dominates linear polarization at these frequencies. Linear polarization is not detected to instrumental limits of 0.1% while circular polarization is detected at levels as high as 1%. This is substantially different from what is seen in high luminosity AGN, where linear always dominates circular polarization (see Homan et al., these proceedings). This property has spawned interest in models that destroy linear polarization and convert linear polarization into circular polarization through Faraday effects (see Beckert et al. and Ruszkowski et al., these proceedings). These models give us a handle on the low energy end of the electron spectrum as welll as the magnetic field geometry. The fractional circular polarization spectrum is highly variable. In a flaring state, the spectral index is inverted with a maximum value of +1 between 8.4 and 15 GHz. This suggests that circular polarization could be detected at very high frequencies but this has not been seen yet.