Optical emission and particle acceleration in a quasi-stationary component in the jet of OJ 287
Sasada, Mahito; Jorstad, Svetlana; Marscher, Alan P.; Bala, Vishal; Joshi, Manasvita; MacDonald, Nicholas R.; Malmrose, Michael P.; Larionov, Valeri M.; Morozova, Daria A.; Troitsky, Ivan S.; Agudo, Ivan; Casadio, Carolina; Gomez, Jose L.; Molina, Sol N.; Itoh, Ryosuke
We analyze the linear polarization of the relativistic jet in BL Lacertae object OJ 287 as revealed by multi-epoch Very Long Baseline Array images at 43 GHz and monitoring observations at optical bands. The electric-vector position angle of the optical polarization matches that at 43 GHz at locations that are often in the compact millimeter-wave "core" or, at other epochs, coincident with a bright, quasi-stationary emission feature ~0.2 mas (~0.9 pc projected on the sky) downstream from the core. This implies that electrons with high enough energies to emit optical synchrotron and γ-ray inverse Compton radiation are accelerated both in the core and at the downstream feature, the latter of which lies ≥10 pc from the central engine. The polarization vector in the stationary feature is nearly parallel to the jet axis, as expected for a conical standing shock capable of accelerating electrons to GeV energies.
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