THE RADIO GALAXY PICTOR-A - A STUDY WITH THE VLA

Detailed multi-frequency VLA observations of the prominent southern ra dio galaxy Pictor A are described. The radio structure is found to com prise very dim, nearly circular lobes with an extraordinarily bright a nd compact hot spot located at the western extremity of the western lo be. A faint jet is observed to connect this hot spot with the radio nu cleus. No counter-jet is seen. The eastern lobe contains two hot spots of much lesser brightness and compactness. The radio lobes have signi ficantly different spectral indices, with the eastern (un-jetted) lobe being 'steeper'. Enhanced spectral steepening is found in the central regions surrounding the radio nucleus, and around the peripheries of both radio lobes. The eastern lobe depolarizes at a higher frequency t han the western lobe, and also displays a much higher rms scatter in t he derived rotation measure, although the mean rotation measure is ver y similar in both lobes. Steepening of the high frequency spectral ind ex (lambda 6 cm to lambda 2 cm) is seen in the lobe near to the wester n hot spot. From the similarity in the structure of the western hot sp ot - including the extended filament - between radio and optical wavel ength ranges it is concluded that all of the extended optical emission is due to the synchrotron process. The implications of these findings are discussed.