Parsec-scale Faraday rotation distribution in the BL Lac object 1803+784

• Published in: Monthly notices of the Royal Astronomical Society Vol. 339; no. 3; pp. 669 - 679
• Main Authors: Gabuzda, D. C., Chernetskii, V. A.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01-03-2003
• Subjects: BL Lacertae objects: individual: 1803 + 784; polarization; radio continuum: galaxies; polarization; radio continuum: galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1046/j.1365-8711.2003.06204.x

We present the results of VLBI polarization observations of the BL Lac object 1803+784 made simultaneously at 22, 15, 8 and 5 GHz in 1997 April, and quasi-simultaneously at 1.6 and 5 GHz in 1998 July. These data have yielded the total intensity, polarization, spectral-index, and rotation-measure distributions on scales from less than 1 mas to about 30 mas from the core (from a projected distance of about 1–150 pc at the redshift of 1803+784). There is an enhancement in the rotation measure for the VLBI core, clearly due to plasma in the immediate vicinity of the AGN. The rotation measures 10–30 mas from the core demonstrate that the Galactic contribution to the total observed rotation measures is equal to the previously reported integrated rotation measure (−61 rad m−2). After subtracting this Galactic contribution and multiplying by (1 +z)2, the rotation measure for the VLBI core in the source rest frame is about 500 rad m−2, similar to the VLBI core rotation measures reported previously for BL Lac and several quasars.