SIMBAD references

Aims. We present a multifrequency, dense radio monitoring program of the blazar OJ 287 using the 100-m Effelsberg radio telescope. The program aims to test different binary supermassive black hole (SMBH) scenarios and studying the physical conditions in the central region of this bright blazar. Here, we analyze the evolution in total flux density, linear and circular polarization as a means to study the OJ 287 jet structure and its magnetic field geometry.
Methods. We used a recently developed, high-precision data analysis methodology to recover all four Stokes parameters. We measured the total flux density of OJ 287 at nine bands from 2.64GHz to 43GHz, the linear polarization parameters at four bands between 2.64GHz and 10.45GHz, and the circular polarization at two bands, 4.85GHz and 8.35GHz. The mean cadence of our measurements is ten days.
Results. Between December 2015 and January 2017 (MJD 57370-57785), OJ 287 showed flaring activity and complex linear and circular polarization behavior. The radio electric vector position angle (EVPA) showed a large clockwise (CW) rotation by ∼340° with a mean rate of -1.04°/day. Based on concurrent very long baseline interferometric (VLBI) polarization data at 15GHz and 43GHz, the rotation seems to originate within the jet core at 43GHz (projected angular size ≤0.15mas or 0.67pc at the redshift of the source). Moreover, optical polarization data show a similar monotonic CW rotation with a rate of about -1.1°/day which is superposed with shorter and faster rotations that exhibit rates of about 7.8°/day, mainly in the CW sense.
Conclusions. The flux density and polarization variability of the single dish, VLBI and optical data is consistent with a polarized emission component propagating on a helical trajectory within a bent jet.