HST images of the western hot spot of the nearby FR Ⅱ radio galaxy Pictor A resolve the hot spot into an amorphous region of highly polarized wisps. The high polarization (approx > 50%) indicates that the optical emission is synchrotron radiation and that the magnetic field structure has been well resolved. The magnetic field is oriented nearly perpendicular to the jet axis and apparently very uniform. We interpret these observations in terms of a compressed magnetic field at the working surface where the jet impinges on the intergalactic medium some 100 kpc from the nucleus of the host galaxy.
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