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Session 56 - BL Lacs & Blazars.
Oral session, Thursday, January 08
Georgetown,
We have carried out polarimetric imaging at 7 mm of a small sample of blazars with the VLBA. The sub-milliarcsecond resolution of the images has allowed us to investigate the magnetic field properties very close to the cores of these objects. At mm-wavelengths, we find no appreciable differences between the BL Lacs and quasars in our sample, in contrast to the situation at longer wavelengths, where the jets of BL Lacs tend to have electric vector position angles (EVPAs) that are parallel to the jet axis. In all five high-optical polarization objects in which core polarized emission was detected, the EVPA of the core was aligned with the local jet direction, most likely as a result of strongly shocked regions below the resolution level of our images. We discuss how component blending at low resolution can have a large effect on the observed polarization structure of the core region.
We also have detected two classes of polarized components in the jets of blazars: the first with EVPAs aligned closely with the local jet direction, and a second class with EVPAs at an oblique angle between 40 and 60 degrees. We discuss the effects of oblique shocks, relativistic aberration, and flux density bias on the observed EVPAs of these polarized components.
