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日内可变源J1128 +592的甚长基线阵列观测

Very Long Baseline Array observations of the Intraday Variable source J1128+592

K. E. Gabanyi, N. Marchili, T. P. Krichbaum, L. Fuhrmann, P. Muller, J. A. Zensus, X. Liu, H. G. Song

备注：
accepted for A&A (11 pages, 11 figures)
发表信息：
Astronomy and Astrophysics, Volume 508, Issue 1, 2009, pp.161-171
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摘要：

平谱射电源的短时间尺度通量密度变化通常被解释为银河系湍流电离星际物质中无线电波的散射。支持这一观点的最有说服力的观测论据之一是地球围绕太阳的轨道运动引起的变率时间尺度的年度调制。J1128+592是一个IDV源，其变率时间尺度可能存在年调制。我们观察了6个时代的VLBA在5，8和15 GHz的总强度和偏振的源。VLBA观测揭示了一个东西向的核心喷流结构。它的位置角与由年调制模型导出的各向异性角一致。在质量尺度上，VLBI没有观测到明显的长期结构变化，但是，与档案数据相比，VLBI核心尺寸扩大了。这种扩张为观察到的IDV强度降低提供了可能的解释。VLBI偏振测量表明，地核和喷流的电矢量位置角和旋转量发生了显著变化。所观察到的RM的变化的一部分可以归因于散射屏幕（37 pc的距离），其中包括源（核心和射流），这可能是负责IDV。偏振子分量的叠加低于角分辨率极限也可能影响所观察到的RM。

英文摘要：

Short time-scale flux density variations of flat spectrum radio sources are often explained by the scattering of radio waves in the turbulent, ionized Interstellar Matter of the Milky Way. One of the most convincing observational arguments in favor of this is the annual modulation of the variability time-scale caused by the Earth orbital motion around the Sun. J1128+592 is an IDV source with a possible annual modulation in its variability time-scale. We observed the source in 6 epochs with the VLBA at 5, 8 and 15 GHz in total intensity and polarization. The VLBA observations revealed an east-west oriented core-jet structure. Its position angle agrees with the angle of anisotropy derived from the annual modulation model. No significant long-term structural changes were observed with VLBI on mas-scales, however, compared to archival data, the VLBI core size is expanded. This expansion offers a possible explanation to the observed decrease of the strength of IDV. VLBI polarimetry revealed significant changes in the electric vector position angle and Rotation Measure of the core and jet. Part of the observed RM variability could be attributed to a scattering screen (37 pc distance), which covers the source (core and jet) and which may be responsible for the IDV. Superposition of polarized sub-components below the angular resolution limit may affect the observed RM as well.

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