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Astron. Astrophys. 328, 12-32

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The radio galaxy Pictor A - a study with the VLA

Richard A. Perley1, Hermann-Josef Röser2, and Klaus Meisenheimer2

1National Radio Astronomy Observatory*, Socorro, NM 87801, USA
2Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany

Received 10 March 1997 / Accepted 20 May 1997


Detailed multi-frequency VLA observations of the prominent southern radio galaxy Pictor A are described. The radio structure is found to comprise very dim, nearly circular lobes with an extraordinarily bright and compact hot spot located at the western extremity of the western lobe. A faint jet is observed to connect this hot spot with the radio nucleus. No counter-jet is seen. The eastern lobe contains two hot spots of much lesser brightness and compactness. The radio lobes have significantly 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 than the western lobe, and also displays a much higher rms scatter in the derived rotation measure, although the mean rotation measure is very similar in both lobes. Steepening of the high frequency spectral index (6 cm to 2 cm) is seen in the lobe near to the western hot spot.

From the similarity in the structure of the western hot spot - including the extended filament - between radio and optical wavelength ranges it is concluded that all of the extended optical emission is due to the synchrotron process. The implications of these findings are discussed.

Key words: Acceleration of particles - polarization - radiation mechnisms: non-thermal - galaxies: Pictor A - radio continuum: galaxies

*The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation.

© European Southern Observatory (ESO) 1997

Online publication: October 30, 1997
Last change: March 24, 1998