The Magnetic Field near the Galactic Center

Multichannel, narrow-band polarimetric observations at 5 GHz of the galactic center region have been made using the Effelsberg 100-m telescope. Polarization structures near the radio arc are basically consistent with previous 10-GHz observations, but there exists a significant discrepancy in position and rotation measure characteristics between 5 and 10 GHz for the polarized emission on the radio arc. This indicates a complicated internal Faraday rotation in the arc. The distributions of rotation measure across the galactic plane and across the rotation axis of the Galaxy suggest the existence of a large-scale poloidal magnetic field twisted by the disk rotation. A primordial origin is suggested for the poloidal field. Some polarization was found on the edges of the radio bridge, that connects the radio arc with Sgr A, and a Faraday rotation reaching |RM| ~ 103 rad m-2 was recorded, whereas the bridge center is depolarized. This fact shows for the first time the magnetoionic characteristics of the radio bridge.