The polarisation behaviour of OJ 287 viewed through radio, millimetre and optical observations between 2015 and 2017

TL;DR

This study analyzes the polarisation behaviour of blazar OJ 287 from 2015 to 2017 across radio, millimetre, and optical wavelengths, linking observed flares and jet activity to potential supermassive black hole binary interactions.

Contribution

It provides a multi-wavelength polarimetric analysis of OJ 287, revealing connections between optical flares, jet components, and gamma-ray activity, with new insights into jet substructures and component speeds.

Findings

Optical flare coincided with a 210-degree polarisation angle rotation.

A new jet component K was identified with a speed of 0.12 mas/yr.

Jet substructures are traced differently in mm and cm bands during component passage.

Abstract

OJ 287 is a bright blazar with century-long observations, and one of the strongest candidates to host a supermassive black hole binary. Its polarisation behaviour between 2015 and 2017 (MJD 57300-58000) contains several interesting events that we re-contextualise in this study. We collected optical photometric and polarimetric data from several telescopes and obtained high-cadence light curves from this period. In the radio band, we collected mm-wavelength polarisation data from the AMAPOLA program. We combined these with existing multifrequency polarimetric radio results and the results of very-long-baseline-interferometry imaging with the Global mm-VLBI Array at 86 GHz. In December 2015, an optical flare was seen according to the general relativistic binary black hole model. We suggest that the overall activity near the accretion disk and the jet base during this time may be connected to the onset of a new moving component K seen in the jet in March 2017. With the additional optical data, we find a fast polarisation angle rotation of 210 degrees coinciding with the December 2015 flare, hinting at a possible link between these events. Based on the 86-GHz images, we calculated a new speed of 0.12 mas/yr for K, which places it inside the core at the time of the 2015 flare. This speed also supports the scenario where the passage of K through the quasi-stationary feature S1 could have been the trigger for the very-high-energy gamma-ray flare of OJ 287 seen in February 2017. With the mm-polarisation data, we established that these bands follow the cm-band data but show a difference during the time of K passing through S1. This indicates that the mm-bands trace the substructures of the jet still unresolved in the cm-bands.