Optical polarization angle and VLBI jet direction in the binary black hole model of OJ287

TL;DR

This paper models the optical polarization angle and jet direction in blazar OJ287 using a binary black hole framework with a stable magnetic field, aligning well with observed data and suggesting a large-scale helical magnetic field.

Contribution

It introduces a combined model linking jet precession, optical brightness, and polarization angle variations in OJ287 within a binary black hole context.

Findings

Model fits the polarization data well with a nearly parallel magnetic field.

Supports the presence of a large-scale helical magnetic field in the jet.

Aligns jet precession with optical and radio observations.

Abstract

We study the variation of the optical polarization angle in the blazar OJ287 and compare it with the precessing binary black hole model with a 'live' accretion disk. First, a model of the variation of the jet direction is calculated, and the main parameters of the model are fixed by the long term optical brightness evolution. Then this model is compared with the variation of the parsec scale radio jet position angle in the sky. Finally, the variation of the polarization angle is calculated using the same model, but using a magnetic field configuration which is at a constant angle relative to the optical jet. It is found that the model fits the data reasonably well if the field is almost parallel to the jet axis. This may imply a steady magnetic field geometry, such as a large-scale helical field.