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Paper: Radio Polarization and Flux Density Variability of BL Lacertae: Oblique Shocks
Volume: 159, BL Lac Phenomenon
Page: 45
Authors: Aller, H. D.; Hughes, P. A.; Freedman, I.; Aller, M. F.
Abstract: The results of more than 20 years of UMRAO multifrequency single antenna observations are presented which reveal a series of highly polarized outbursts. Comparison with VLBI maps shows that for many bursts the plane of the electric vector of the polarized emission is parallel to the observed jet structure, and several of these bursts have been quantitatively modeled by weak, transverse shocks propagating along a relativistic flow. However, in the past decade the polarization position angle has exhibited variations of tens of degrees from burst to burst during time periods when VLBI observations by Mutel and others have shown curvature in the radio jet structures. During periods when VLBI revealed new components, whose direction of propagation deviated by ten or more degrees from the average direction, the polarization position angles deviated in the same direction by even larger values. This behavior suggests the presence of oblique shocks. The degree and direction of polarization together with our total flux data are used to constrain the possible strength, obliquity and orientation of the shock fronts. This work was supported in part by NSF Grant AST950178.
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