We explore the variability and cross-frequency correlation of the flux density and polarization of the blazar OJ287 , using imaging at 43 GHz with the Very Long Baseline Array , as well as optical and near-infrared polarimetry .
The polarization and flux density in both the optical waveband and the 43 GHz compact core increased by a small amount in late 2005 , and increased significantly along with the near-IR polarization and flux density over the course of 10 days in early 2006 .
Furthermore , the values of the electric vector position angle ( EVPA ) at the three wavebands are similar .
At 43 GHz , the EVPA of the blazar core is perpendicular to the flow of the jet , while the EVPAs of emerging superluminal knots are aligned parallel to the jet axis .
The core polarization is that expected if shear aligns the magnetic field at the boundary between flows of disparate velocities within the jet .
Using variations in flux density , percentage polarization , and EVPA , we model the inner jet as a spine-sheath system .
The model jet contains a turbulent spine of half-width 1.2 \arcdeg and maximum Lorentz factor of 16.5 , a turbulent sheath with Lorentz factor of 5 , and a boundary region of sheared field between the spine and sheath .
Transverse shocks propagating along the fast , turbulent spine can explain the superluminal knots .
The observed flux density and polarization variations are then compatible with changes in the direction of the inner jet caused by a temporary change in the position of the core if the spine contains wiggles owing to an instability .
In addition , we can explain a stable offset of optical and near-IR percentage polarization by a steepening of spectral index with frequency , as supported by the data .