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Paper: The Parsec Scale Radio Jet of 4C 39.25: Witnessing the Interaction between a Superluminal and Stationary Component
Volume: 159, BL Lac Phenomenon
Page: 452
Authors: Alberdi, A.; Gomez, J.-L.; Marcaide, J. M.; Perez-Torres, M. A.; Marscher, A. P.
Abstract: We present multi-epoch 15, 22 and 43 GHz VLBA polarimetric radio observations of the quasar 4C39.25. With these observations we have been able to: - - Study the geometry of the parsec scale jet of 4C39.25 through the monitoring of the evolution of the total flux density, the polarized flux density and -above all- the polarization angle of the region associated with components {a} and {b}; this is of special relevance now that we have found evidence in favour of an immediate, or perhaps ongoing, "collision" between the superluminal component {b} and the region associated with the stationary component {a}: i) at millimeter and centimeter wavelengths, the total flux density light curve has reached a "plateau" at its maximum value while the polarized flux density is already decreasing, and ii) the proper motion of 4C39.25 with respect to the quasi-inertial reference frame defined by the sources observed in the USNO-programme shows a sharp change in the slope. Compare the orientation of the magnetic field between the bent portions of the jet (associated to components {a} and {c}) and the superluminal component (component {b}), allowing us to determine the nature of the stationary components as standing shocks produced by curvatures in the jet or due to interactions with the surrounding medium.
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