Multi-frequency VLBA Polarimetry of the high-redshift GPS Quasar OQ172
Multi-frequency VLBA Polarimetry of the high-redshift GPS Quasar OQ172
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DOI：
10.1093/mnras/stx617
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发表时间：
2017-03
影响因子：
4.8
通讯作者：
Yi Liu;D. Jiang;M. Gu;L. Gurvits
中科院分区：
文献类型：
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作者：
Yi Liu;D. Jiang;M. Gu;L. Gurvits
2005年对GPS （GPS）类星体OQ172 （J1445+0958）在1.6、2.2、4.8、8.3和15.3 GHz波段进行了多频甚长基线阵列（VLBA）偏振观测。在距离地核约3mas处，在所有波段都能探测到强烈弯曲的喷流结构。源的射电发射在所有五个波段都极化。我们研究了所有五个波段的核心和射流组件的法拉第旋转，发现4.8 GHz和8.3 GHz的核心和射流组件的法拉第旋转具有良好的线性拟合。在这两个频率下，旋转测量（RM）在核心为$\sim 2000~\ RM rad~m^{-2}$，在内部射流部件为$\sim 700~\ RM rad~m^{-2}$，在外部射流部件继续减小。我们发现4.8 GHz和8.3 GHz的去极化可能是由源内介质引起的。我们研究了VLBI组件的周转光谱与同步加速器自吸收（SSA）和自由-自由吸收（FFA）模型的一致性。虽然由于缺乏低频数据，这两种模型不容易区分，但每种模型的物理参数都是可以约束的。我们发现$\rm [OIII]_{5007}$线的大宽度可能是由射流与窄线区域（NLR）介质相互作用引起的。射流弯曲、显著的RM变化、法拉第去极化、光谱翻转和$\ RM [OIII]_{5007}$的宽谱线宽度可能密切相关，可能是由相同的核介质引起的，可能是NLR。
Multi-frequency Very Long Baseline Array (VLBA) polarimetry observation of the GHz-Peaked Spectrum (GPS) quasar OQ172 (J1445+0958) has been performed at 1.6, 2.2, 4.8, 8.3 and 15.3 GHz in 2005. Core-jet structures are detected in all bands with the jet strongly bent at about 3 mas from the core. The radio emission of the source is polarised at all five bands. We study the Faraday Rotation in the core and jet components at all five bands, and find good linear fits of Faraday Rotation in the core and jet components at 4.8 and 8.3 GHz. At these two frequencies, the Rotation Measure (RM) is $\sim 2000~\rm rad~m^{-2}$ in the core and $\sim 700~\rm rad~m^{-2}$ in the inner jet components and continues to decrease at the outer jet parts. We find that the depolarisation at 4.8 and 8.3 GHz might be caused by the internal medium in the source. We investigate consistency of the turnover spectra of VLBI components with the Synchrotron Self-Absorption (SSA) and Free-Free Absorption (FFA) models. Although these two models can not be easily distinguished due to the lack of low-frequency data, the physical parameters can be constrained for each model. We find that the large width of the $\rm [OIII]_{5007}$ line is likely caused by a jet interaction with a Narrow Line Region (NLR) medium. The jet bending, significant RM variations, Faraday depolarisation, spectral turnover, and broad line width of $\rm [OIII]_{5007}$ could be closely related, likely caused by the same nucleus medium, presumably NLR.