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H.D Aller, M.F. Aller, P.A. Hughes (U. Mich.), J.F.C. Wardle, D.C. Homan, D.H. Roberts (Brandeis U.)
We present multi-epoch VLBI images and single antenna monitoring results for highly variable extragalactic sources from a program to study evolving source structures in order to investigate the possible role of oblique shocks in the relativistic flows of AGN jets. Since July 1999, we have obtained total intensity and polarization measurements with the VLBA at 15 and 43~GHz at five epochs together with weekly observations of integrated total flux and linear polarization with the University of Michigan 26-meter paraboloid at 4.8, 8.0 and 14.5~GHz. A subset of the sources known to exhibit significant opacity effects were also mapped at 8 and 22~GHz. The sample is comprised of 11 objects found by the UMRAO variability program to exhibit frequent, high-amplitude, temporally-resolved outbursts and contains a mix of sources with long-term preferred magnetic field orientation ranging from parallel to perpendicular to the overall jet structure. Eight of the sources exhibited new outbursts during the mapping period: 0133+476, 0215+015, 0607-157, OJ~287, 1510-089, 1749+096, 1928+738, and BL Lac; the other three objects (1055+018, 3C 279, and 3C 446), are exhibiting long term outbursts.
This work was suported in part by NSF grant AST-9900723. The UMRAO is supported by the University of Michigan; The National Radio Astronomy Observatory is operated by Associated Universities, Inc, under cooperative agreement with the National Science Foundation.
The author(s) of this abstract have provided an email address for comments about the abstract: haller@umich.edu