AAS 199th meeting, Washington, DC, January 2002
Session 98. Blazars and Other AGN Jets
Display, Wednesday, January 9, 2002, 9:20am-6:30pm, Exhibit Hall

## [98.07] Multi-frequency, Multi-epoch VLBA Polarimetry Observations of the Blazar J1058+0133

L. K. Pollack (University of California, Berkeley), J. M. Attridge (MIT Haystack Observatory), J. F. C. Wardle (Brandeis University)

In 1997 observations at 5~GHz with the VLBA, J1058+0133 revealed a distinctive two-component jet with a boundary layer or sheath'' never before seen in any blazar on milli-arcsecond scales (Attridge, Roberts, & Wardle 1999). Images of this source show that the magnetic field in the sheath is oriented longitudinally to the jet axis, while the magnetic field in the central jet or spine'' is oriented transverse to the jet axis.

VLBI studies of blazars at centimeter wavelengths suggest that weak-lined sources (commonly BL Lacertae objects or BL~Lacs) differ from strong-lined sources (commonly quasars) in the orientations of their magnetic fields (Cawthorne et al. 1993). BL~Lacs display magnetic fields oriented longitudinal to the jet axis, while quasars display a transverse magnetic field. J1058+0133 lies on the borderline between weak- and strong-lined sources {\em and} displays simultaneous orthogonal polarization angles, providing a unique opportunity to study shocked jet models and the relationship between magnetic field orientations and optical designations of blazars.

Here we present preliminary VLBA total intensity and polarization data of J1058+0133, confirming the sheath-spine structure at multiple frequencies and multiple epochs.

This research was carried out as part of the National Science Foundation's Research Experience for Undergraduates (REU) Program at MIT Haystack Observatory.