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.
