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H.D. Aller, M.F. Aller, P.A. Hughes (U. Mich.), J.F.C. Wardle, D.H. Roberts (Brandeis U.), D.C. Homan (NRAO)
We present multi-epoch VLBI images and single antenna monitoring results from a study of 10 highly variable AGNs (BL~Lacs and QSOs) whose primary goal is to investigate the strengths and orientations of oblique shocks in relativistic flows by comparing observed polarized features found in VLBA total intensity and polarization images and UMRAO monitoring data with the predictions of simple oblique shock models which account for the effects of relativistic aberration. The data consist of weekly observations at 14.5, 8.0 and 4.8 GHz using the UMRAO 26-meter telescope, and seven sets of VLBA total flux and polarization images spaced over the past two years at 15 and 43 GHz supplemented by maps at 8 and 22 GHz for a subset known to exhibit significant opacity. The morphological evolution in both structure and polarization revealed by these data are used to provide an estimation of the projected flow deviation and magnetic field orientation at shocks, and initial results from a comparison of the data with newly developed radiative transfer models allowing for a range of shock orientations are presented.
This work was supported 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.