Paper detail

Polarization behavior of periodic optical outbursts in blazar OJ287

As a characteristic feature of generic blazars the polarization behavior of the quasi-periodic optical outbursts observed in OJ287 is investigated. The optical light-curves of the December/2015 outburst are also simulated in terms of the precessing jet nozzle model previously proposed. The polarization behavior of three primary quasi-periodic optical outbursts peaking in 1983.0, 2007.8 and 2015.8 are analyzed in order to understand the nature of their optical radiation. A two-component model has been applied,showing that the variations in flux density, polarization degree and polarization position angle can be consistently interpreted with two polarized components: one steady-component with constant polarization and one burst-component with varying polarization (e.g., relativistic shock propagating along the jet-beam axis). The flux light curves of the December/2015 outburst (including its first flare and second flare) are well model-simulated in terms of 14 elementary synchrotron sub-flares, each having a symmetric profile. The model simulations of polarization behavior for the three major outbursts (in 1983.0, 2007.8 and 2015.8) demonstrate that they all exhibit rapid and large rotations in polarization position angle, implying that they are synchrotron flares produced in the jet. Combining with the results previously obtained for interpreting the optical light curves in terms of lighthouse effect for both quasi-periodic and non-periodic outbursts, we suggest that relativistic jet models may be the most appropriate models for understanding the nature of the optical flaring radiation in blazar OJ287: its optical outbursts may comprise a number of blended "elementary synchrotron flares" , each produced by the helical motion of individual superluminal optical knots via lighhouse effect.