发表机构
National Astronomical Research Institute of Thailand (Public Organization); Institute of Astronomy and Astrophysics, Academia Sinica; Department of Physics and Astronomy, Seoul National University; SNU Astronomy Research Center, Seoul National University; National Astronomical Observatory of Japan; Division of Liberal Arts, Kogakuin University of Technology & Engineering; Department of Astronomical Science, The Graduate University for Advanced Studies, SOKENDAI; Joint ALMA Observatory（泰国国家天文研究所; 中央研究院天文及天文物理研究所; 首尔大学物理与天文学系; 首尔大学天文学研究中心; 日本国立天文台; 工学院大学教养学部; 综合研究大学院大学天文学研究科; ALMA联合observatory）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究通过多频监测发现OJ 287在2015-2017年出现大尺度EVPA旋转，并建模表明其由螺旋磁场中单一新扰动传播主导，而非相对论性聚束效应增强所致。
AI 中文摘要
我们利用KVN（22–129 GHz）、ALMA（91.5–343.5 GHz）和Metsähovi（37 GHz）对耀变体OJ 287进行了高频率、多频段的监测，覆盖2012–2023年，并结合已发表的光学偏振测量数据。在这长达十年的数据集中，仅在2015–2017年间观测到一次异常巨大且平滑的EVPA旋转。毫米波段的EVPA在约1.5年内旋转超过约300度，同时在光学波段观测到规模相当且演化更快的旋转，而在其他时期则保持相对稳定。该旋转与一系列从37 GHz到343 GHz的强射电耀发同时发生，这些耀发的峰值振幅在2017年3月（旋转结束时）之前逐渐增大。对ALMA 91.5 GHz光变曲线的建模得出，在EVPA旋转期间，变差多普勒因子δ_var约为8–11，且在整个耀发序列中没有系统性增加。δ_var缺乏单调变化表明，逐渐增强的相对论性聚束效应不太可能是耀发包络上升的主要驱动因素。大尺度EVPA旋转仅限于该时间段，加上δ_var几乎恒定，表明2015–2017年的事件发生在一个新抛射的扰动在传播过程中暂时主导偏振发射，同时穿过由螺旋磁场贯穿的结构化内喷流区域，且喷流方向发生适度变化。因此，大尺度EVPA旋转随着喷流取向的演化而间歇性地出现，并且仅在发射主导性和观测几何有利对齐时才能实现。
英文摘要
We present high-cadence, multi-frequency monitoring of the blazar OJ 287 using KVN (22--129 GHz), ALMA (91.5--343.5 GHz), and Metsähovi (37 GHz), covering 2012--2023, together with published optical polarimetry. Within this decade-long dataset, an exceptionally large and smooth EVPA rotation is observed only during 2015--2017. The millimeter-band EVPA rotates by more than $\sim$300 deg over $\sim$1.5 yr, with a comparably large and more rapidly evolving rotation observed at optical wavelengths, while remaining comparatively stable at other epochs. The rotation coincides with a sequence of strong radio flares from 37 to 343 GHz whose peak amplitudes increase toward 2017 March, when the rotation ends. Modeling the ALMA 91.5 GHz light curve yields variability Doppler factors of $δ_{\rm var} \sim 8$--$11$ during the EVPA-rotation interval, with no systematic increase across the flare sequence. The absence of a monotonic change in $δ_{\rm var}$ indicates that progressively enhanced relativistic beaming is unlikely to be the primary driver of the rising flare envelope. The confinement of the large EVPA rotation to this interval, together with the nearly constant $δ_{\rm var}$, indicates that the 2015--2017 event occurred when a single newly ejected disturbance temporarily dominated the polarized emission while propagating through structured inner-jet regions threaded by a helical magnetic field under modest jet-direction changes. Large EVPA rotations therefore arise intermittently as the jet orientation evolves, and are realized only when emission dominance and viewing geometry align favorably.
Comments25 pages, 13 figures. Accepted for publication in The Astrophysical Journal
