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Extragalactic radio source stability and VLBI celestial reference frame: insights from the Allan standard deviation ?

机译：银河外无线电源稳定性和VLBI天体参考系：来自艾伦标准偏差的见解？ <相关对象object-type =“ tableCDS”源ID =“ http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/618/A80” source-id-type =“ url” />

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Aims . We investigate the composition of the noise in coordinate time series of several hundreds of extragalactic radio sources monitored by the geodetic VLBI program since 1979. The noise type is identified at all available timescales longer than one year, following the observational history of the source. Methods . We computed the Allan standard deviation of coordinate time series and developed a Monte Carlo test to evaluate the influence of the irregular sampling and error on data onto the noise type identification. We classified the radio sources into three categories depending on their type of noise and taking into account the dominating noise at different timescales: from the category AV0, which contains sources with a stable behavior at all timescales, to the category AV2, which contains sources whose coordinates are dominated by random walks at the longest timescales. Results . We found that almost no source exhibited “idealized” white noise. Only 5% of the 647 sources we studied belong to the category AV0 (stable sources). Moreover, we found that this class contains sources with relatively short observational histories, suggesting that after some years, a source whose astrometric position has shown a stable behavior is likely to become unstable. This questions the existence of the stable source paradigm and adds complementary information in the crucial task of selecting sources on which to base the axes of the celestial reference frame.
机译：目的。我们调查了自1979年以来由大地测量VLBI程序监视的数百个河外无线电源的坐标时间序列中的噪声组成。根据该源的观测历史，在超过一年的所有可用时间范围内都可以识别出噪声类型。方法 。我们计算了坐标时间序列的艾伦标准偏差，并开发了蒙特卡洛检验，以评估不规则采样和误差对数据对噪声类型识别的影响。根据无线电源的噪声类型，并考虑到不同时间尺度上的主要噪声，我们将无线电源分为三类：从类别AV0（包含在所有时间尺度上行为稳定的源）到类别AV2（包含在各个时间范围内行为稳定的源）坐标以最长的时间尺度上的随机游走为主。结果。我们发现几乎没有源显示出“理想化”的白噪声。在我们研究的647个源中，只有5％属于AV0类（稳定源）。此外，我们发现该类别包含的观测历史较短的源，表明几年后，其天体位置已显示稳定行为的源可能会变得不稳定。这对稳定源范式的存在提出了质疑，并在选择源的关键任务中增加了补充信息，而源是天体参考系轴的基础。

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