Ju l 2 00 0 Detection and Measurement of Parsec-Scale Circular Polarization in Four AGN
Ju l 2 00 0 Detection and Measurement of Parsec-Scale Circular Polarization in Four AGN
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Jul l 2 00 0 四个活动星系核中秒差距级圆偏振的探测和测量
DOI：
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发表时间：
1999
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通讯作者：
J. Wardle
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作者：
D. Homan;J. Wardle
本文给出了13个活动星系核的5个15 GHz VLBA观测历元。这些观测是专门校准检测秒差距尺度的圆偏振和我们的校准技术进行了详细的讨论和分析。我们在4个活动星系核（3C 84，PKS 0528+134，3C 273和3C 279）的射电喷流中获得了可靠的秒差距尺度圆偏振探测。对于这些物体中的每一个，我们的检测都是在0.3 − 1%的局部分数圆偏振水平。每个单独检测的显著性范围为3至10 σ。我们的观测结果在多个时期（和不同的校准技术）的圆偏振的符号和幅度是一致的。3C 273和3C 279在我们的观测期间都经历了核心爆发，并且两个源的圆偏振的变化与这些爆发相关。在一般情况下，我们观察到的圆偏振几乎与这些对象的强VLBI核心一致，然而，在3C 84的圆偏振位于一个完整的毫角秒南部的源峰，并在1996.73时代的3C 273的圆偏振主要是与新出现的喷流组件。我们的观测结果支持了理论结论，即圆偏振的发射是不透明度的敏感函数，当光学深度接近1时最强。圆偏振可以作为同步辐射的固有分量产生，或者通过线偏振到圆偏振的法拉第转换产生。我们的单频观测并不容易区分这些可能的机制，但独立于机制，所观察到的圆极化符号在整个时代的显着一致性表明存在长期，稳定，单向磁场。Hodge和阿勒在8 GHz对3C 273和3C 279进行的单碟观测表明，在我们的观测框架中，这种稳定性可能会持续数十年。主题标题：星系：喷流-星系：磁场-极化-类星体：个体（3C 84，PKS 0528+134，3C 273，3C 279）jfcw@quasar.astro.brandeis.edu dch@quasar.astro.brandeis.edu
We present five epochs of 15 GHz VLBA observations of 13 AGN. These observations were specially calibrated to detect parsec-scale circular polarization and our calibration techniques are discussed and analyzed in detail. We obtained reliable detections of parsec-scale circular polarization in the radio jets of four AGN: 3C 84, PKS 0528+134, 3C 273, and 3C 279. For each of these objects our detections are at the level of ∼ 0.3 − 1% local fractional circular polarization. Each individual detection has a significance in the range of 3 to 10 σ. Our observations are consistent across multiple epochs (and different calibration techniques) in the sign and magnitude of the circular polarization observed. 3C 273 and 3C 279 both undergo core outbursts during our observations and changes in the circular polarization of both sources are correlated with these outbursts. In general, we observe the circular polarization to be nearly coincident with the strong VLBI cores of these objects; however, in 3C 84 the circular polarization is located a full milli-arcsecond south of the source peak, and in the 1996.73 epoch of 3C 273 the circular polarization is predominately associated with the newly emerging jet component. Our observations support the theoretical conclusion that emission of circular polarization is a sensitive function of opacity, being strongest when the optical depth is near unity. Circular polarization may be produced as an intrinsic component of synchrotron radiation or by the Faraday conversion of linear to circular polarization. Our single frequency observations do not easily distinguish between these possible mechanisms, but independent of mechanism, the remarkable consistency across epoch of the sign of the observed circular polarization suggests the existence of a long term, stable, uni-directional magnetic field. Single dish observations of 3C 273 and 3C 279 at 8 GHz by Hodge and Aller suggest that this stability may persist for decades in our frame of observation. Subject headings: galaxies: jets — galaxies:magnetic fields — polarization — quasars: individual (3C 84, PKS 0528+134, 3C 273, 3C 279) dch@quasar.astro.brandeis.edu jfcw@quasar.astro.brandeis.edu