OPTICAL STRUCTURE AND POLARIZATION OF THE WESTERN HOT-SPOT OF PICTOR-A

HST images of the western hot spot of the nearby FR II radio galaxy Pi ctor A resolve the hot spot into an amorphous region of highly polariz ed wisps. The high polarization (greater than or similar to 50%) indic ates that the optical emission is synchrotron radiation and that the m agnetic field structure has been well resolved. The magnetic field is oriented nearly perpendicular to the jet axis and apparently very unif orm. We interpret these observations in terms of a compressed magnetic held at the working surface where the jet impinges on the intergalact ic medium some 100 kpc from the nucleus of the host galaxy.