A helical jet model for OJ287

TL;DR

This paper proposes a helical jet model for the quasar OJ287, explaining its complex radio jet structure and optical brightness variations through jet wobble and relativistic effects linked to a binary black hole system.

Contribution

The study introduces a helical jet model that accounts for observed jet structures and brightness variations by linking jet wobble to binary black hole orbital motion.

Findings

Model reproduces observed jet structure and brightness variations.

Relativistic propagation of axis changes explains multi-scale observations.

Helical jet axis varies with speed about 0.85c, matching observed data.

Abstract

Context. OJ287 is a quasar with a quasi-periodic optical light curve, with the periodicity observed for over 120 years. This has lead to a binary black hole model as a common explanation of the quasar. The radio jet of OJ287 has been observed for a shorter time of about 30 years. It has a complicated structure that varies dramatically in a few years time scale. Aims. Here we propose that this structure arises from a helical jet being observed from a small and varying viewing angle. The viewing angle variation is taken to be in tune with the binary orbital motion. Methods. We calculate the effect of the secondary black hole on the inner edge of the accretion disk of the primary using particle simulations. We presume that the axis of the helix is perpendicular to the disk. We then follow the jet motion on its helical path and project the jet to the sky plane. This projection is compared with observations both at mm waves and cm waves. Results. We find that this model reproduces the observations well if the changes in the axis of the conical helix propagate outwards with a relativistic speed of about 0.85c. In particular, this model explains at the same time the long-term optical brightness variations as varying Doppler beaming in a component close to the core, i.e. at parsec scale in real linear distance, while the mm and cm radio jet observations are explained as being due to jet wobble at much larger (100 parsec scale) distances from the core.