Aligning VLBI images of active galactic nuclei at different frequencies
Aligning VLBI images of active galactic nuclei at different frequencies
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DOI：
10.1111/j.1365-2966.2008.13087.x
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发表时间：
2008-05
影响因子：
4.8
通讯作者：
S. Croke;D. Gabuzda
中科院分区：
文献类型：
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作者：
S. Croke;D. Gabuzda
研究河外射电源特性的许多重要技术，如光谱指数和旋转测量测绘，都涉及到两个或多个频率的图像比较。在无线电干涉测量数据的情况下，这可以通过比较在不同频率获得的CLEAN地图来完成。然而，由于无线电发射的频率依赖性而导致的图像中的固有差异可能被由于源可变性而产生的附加差异所扭曲（如果要比较的数据是在不同时间获得的），图像未对准，以及对弱发射的灵敏度和观测提供的角分辨率的频率依赖性（干涉仪的分辨率取决于以观测波长为单位的基线长度）。在应用多频数据比较技术之前，必须尽可能地纠正这些影响。我们考虑上述因素的起源，概述了用于克服这些困难的标准技术，并详细描述了我们开发的一种技术，该技术基于广泛应用于其他领域的互相关技术，用于校正不同频率下的地图之间的不对齐。
Many important techniques for investigating the properties of extragalactic radio sources, such as spectral-index and rotation-measure mapping, involve the comparison of images at two or more frequencies. In the case of radio interferometric data, this can be done by comparing the CLEAN maps obtained at the different frequencies. However, intrinsic differences in images due to the frequency dependence of the radio emission can be distorted by additional differences that arise due to source variability (if the data to be compared are obtained at different times), image misalignment, and the frequency dependence of the sensitivity to weak emission and the angular resolution provided by the observations (the resolution of an interferometer depends on the lengths of its baselines in units of the observing wavelength). These effects must be corrected for as best as possible before multifrequency data comparison techniques can be applied. We consider the origins for the aforementioned factors, outline the standard techniques used to overcome these difficulties, and describe in detail a technique developed by us, based on the cross-correlation technique widely used in other fields, to correct for misalignments between maps at different frequencies.