2002ApJ...573..496T

We present 11 maps of BL Lacertae object 1803+784 derived from geodetic VLBI observations archived at the Washington Correlator. The observations were obtained during the years 1988-1999. In this period three superluminal components with an expansion rate of 0.084 mas.yr^–1 were identified. A remarkable feature of the VLBI images is that the superluminal components only become visible on the jet at a radius of 1 mas from the core, which was interpreted as a result of a helically curved jet. This feature and further evidence of helical patterns found in published high dynamic range VLBI maps at parsec scale and kiloparsec scale enabled us to obtain a well-constrained helical jet. The overall radio morphology of 1803+784 could be described by two dominant components given by a narrow helical jet extending east-west about 6 kpc from the core (deprojected size of 30 kpc) and a much larger north-south component perpendicular to the helical jet (cone axis) with a linear size of about 270 kpc.