OJ 287的高节奏、线性和圆极化监测-弯曲射流中的螺旋磁场
High cadence, linear and circular polarization monitoring of OJ 287 - Helical magnetic field in a bent jet
摘要：
我们提出了一个多频，密集的无线电监测计划的blazar OJ 287使用100米Effelsberg射电望远镜。我们分析了总磁通密度、线极化和圆极化的演化，以研究喷流结构及其磁场几何形状。在2.64 ~ 43 GHz的9个频段上测量了总通量密度，在2.64 ~ 10.45 GHz的范围内测量了线极化参数，在4.85 GHz和8.35 GHz的范围内测量了圆极化参数。平均周期为10天。在MJD 57370和57785之间，OJ 287表现出耀斑活动和复杂的线性和圆偏振行为。无线电EVPA显示顺时针（CW）旋转约340 $^{\circ}$，平均速率为-1.04 $^{\circ}$ /天。基于同时VLBI数据，旋转似乎起源于43 GHz的喷流核心（预计大小$\le$ 0.15 mas或0.67 pc）。此外，光学数据显示了类似的单调CW EVPA旋转，其速率约为-1.1 $^{\circ}$ /天，其与约7.8 $^{\circ}$ /天的较短和较快的旋转叠加。所观察到的变化是一致的偏振发射组件内的弯曲射流的螺旋轨迹上传播。我们将螺旋弧长限制为0.26 pc，半径限制为$\le$ 0.04 pc，以及投射在天空平面上的射流弯曲弧长限制为$\le$ 1.9-7.6 pc。在高角分辨率的VLBI图像中，在喷流的最内侧区域也观察到类似的弯曲。我们的研究结果还表明，存在一个稳定的偏振发射分量与EVPA（-10 $^{\circ}$）垂直的大尺度射流，极向磁场分量的优势。最后，EVPA旋转与光学耀斑同时开始，因此两者可能物理连接。这种光学耀斑与次级SMBH与内部吸积盘的相互作用有关，或者起源于初级SMBH的喷流。
英文摘要：
We present a multi-frequency, dense radio monitoring program of the blazar OJ287 using the 100m Effelsberg radio telescope. We analyze the evolution in total flux density, linear and circular polarization to study the jet structure and its magnetic field geometry. The total flux density is measured at nine bands from 2.64 GHz to 43 GHz, the linear polarization parameters between 2.64 GHz and 10.45 GHz, and the circular polarization at 4.85 GHz and 8.35 GHz. The mean cadence is 10 days. Between MJD 57370 and 57785, OJ287 showed flaring activity and complex linear and circular polarization behavior. The radio EVPA showed a large clockwise (CW) rotation by ~340$^{\circ}$ with a mean rate of -1.04 $^{\circ}$/day. Based on concurrent VLBI data, the rotation seems to originate within the jet core at 43 GHz (projected size $\le$ 0.15 mas or 0.67 pc). Moreover, optical data show a similar monotonic CW EVPA rotation with a rate of about -1.1 $^{\circ}$/day which is superposed with shorter and faster rotations of about 7.8 $^{\circ}$/day. The observed variability is consistent with a polarized emission component propagating on a helical trajectory within a bent jet. We constrained the helix arc length to 0.26 pc and radius to $\le$ 0.04 pc as well as the jet bending arc length projected on the plane of the sky to $\le$ 1.9-7.6 pc. A similar bending is observed in high angular resolution VLBI images at the innermost jet regions. Our results indicate also the presence of a stable polarized emission component with EVPA (-10$^{\circ}$) perpendicular to the large scale jet, suggesting dominance of the poloidal magnetic field component. Finally, the EVPA rotation begins simultaneously with an optical flare and hence the two might be physically connected. That optical flare has been linked to the interaction of a secondary SMBH with the inner accretion disk or originating in the jet of the primary.
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