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Synchronous Optical and Radio Polarization Variability in the Blazar OJ287
2017-03-13

http://adsabs.harvard.edu/abs/2009ApJ...697..985D

  • Speaker : Sincheol Kang
  • Date : 2017-02-22 14:00 ~ 15:00
  • Place : J331-1
  • Professor : Sang-Sung Lee

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 (near-IR)
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 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.

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