从VLBA和光学偏振数据的联合分析得到的高芯法拉第旋转的提示
Hints of High Core Faraday Rotations from a Joint Analysis of VLBA and Optical Polarization Data
摘要：
虽然射电巨响的活动星系核（AGN）的连续体通常在几乎整个光谱上都由同步辐射控制，但尚不清楚射电和高频辐射是起源于喷流的同一部分还是不同部分。最近已经发现了几种不同的基于偏振数据的无线电-光学相关性，这表明光学和无线电偏振可能密切相关，并且相应的发射区域可能是共空间的（Gabuzda et. al 2006，Jorstad et al. 2007，D 'Arcangelo et al. 2007）我们对大约40个活动星系核样本的光学和VLBA偏振数据的联合分析表明，在对推断的VLBA核心法拉第旋转进行校正后，大多数BL Lac天体和一些类星体具有对准的VLBA核心偏振和光学偏振，尽管许多类星体的VLBA核与光学偏振角之间也没有明显的关系。这可能表明，并不是所有的活动星系核在其喷流中都有光辐射和射电辐射的共空间区域。然而，另一种可能性是，一些7 mm-2 cm VLBA核心的法拉第旋转大约为数万rad/m^2，由于观测到的偏振角中的n*pi模糊性，我们的三频数据不能正确拟合，导致核心法拉第旋转的影响被错误地扣除，从而导致不正确的“零波长”无线电偏振角。Zavala & Taylor（2004）和Jorstad et al.（2007）的秒差距尺度法拉第旋转研究结果支持这种高核心法拉第旋转的可能性。
英文摘要：
Although the continua of radio-loud Active Galactic Nuclei (AGN) are typically dominated by synchrotron radiation over virtually the entire spectrum, it is not clear whether the radio and higher-frequency emission originate in the same or different parts of the jet. Several different radio--optical correlations based on polarization data have been found recently, suggesting that the optical and radio polarization may be closely related, and that the corresponding emission regions may be cospatial (Gabuzda et. al2006, Jorstad et al. 2007, D'Arcangelo et al. 2007) Our joint analysis of optical and VLBA polarization data for a sample of about 40 AGNs shows that, after correction for the inferred VLBA core Faraday rotations, most BL Lac objects and some quasars have aligned VLBA-core and optical polarizations, although many quasars also show no obvious relationship between their VLBA-core and optical polarization angles. This may indicate that not all AGNs have cospatial regions of optical and radio emission in their jets. However, another possibility is that some of the 7mm-2cm VLBA cores have Faraday rotations of the order of several tens of thousand of rad/m^2, which were not properly fit by our three-frequency data due to n*pi ambiguities in the observed polarization angles, leading to incorrect subtraction of the effects of the core Faraday rotation, and so incorrect "zero-wavelength" radio polarization angles. The possibility of such high core Faraday rotations is supported by the results of the parsec-scale Faraday-rotation studies of Zavala & Taylor (2004) and Jorstad et al. (2007).
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