arXiv 0704.08712007-04-06astro-ph

IDV源J1128 +5925是一个新的年调制候选源。

The IDV source J1128+5925, a new candidate for annual modulation?

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

备注：: 15 pages, 9 figures Accepted for publication in Astronomy and Astrophysics
DOI：: 10.1051/0004-6361:20067033

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摘要：

致密河外射电源的短时间尺度射电变化，称为日内变化，至少在某些来源中可以用源外效应来解释，其中变化被解释为银河系湍流ISM引起的无线电波闪烁。支持传播引起的变率的最有说服力的观测论据之一是所谓的特征变率时间尺度的年度调制，这是由于地球的轨道运动。列出了最近发现的高度可变的IDV源J1128+5925的数据。我们研究了这个致密类星体中IDV的频率和时间依赖性。我们测量了全年IDV的特征变率时间尺度，并分析了观测到的变率时间尺度的变化是否与年度调制一致。我们利用MPIfR的100米Effelsberg射电望远镜和乌鲁木齐的25米射电望远镜，在2.7 ~ 10.45GHz之间进行了密集时间采样，监测了J1128+5925的通量密度变率。从10个观察会话，我们确定的变化特性和时间尺度。观测到的J1128+5925的变率时间尺度的显著变化是用各向异性的年调制模型模拟的。观测到的变化的频率依赖性是在很好的协议与星际闪烁的预测。采用一个简单的模型的年调制模型，并使用IDV的频率依赖性，我们推导出一个下限的散射屏的距离和上限的散射源大小。后者与VLBI测得的核尺寸一致。

英文摘要：

Short time-scale radio variations of compact extragalactic radio sources, known as IntraDay Variability, can be explained in at least some sources by a source-extrinsic effect, in which the variations are interpreted as scintillation of radio waves caused by the turbulent ISM of the Milky Way. One of the most convincing observational arguments in favour of propagation-induced variability is the so called annual modulation of the characteristic variability time-scale, which is due to the orbital motion of the Earth. Data for the recently discovered and highly variable IDV source J1128+5925 are presented. We study the frequency and time dependence of the IDV in this compact quasar. We measure the characteristic variability time-scale of the IDV throughout the year, and analyze whether the observed changes in the variability time-scale are consistent with annual modulation. We monitored the flux density variability of J1128+5925 with dense time sampling between 2.7 and 10.45GHz with the 100m Effelsberg radio telescope of the MPIfR and with the 25m Urumqi radio telescope. From ten observing sessions, we determine the variability characteristics and time-scales. The observed pronounced changes of the variability time-scale of J1128+5925 are modelled with an anisotropic annual modulation model. The observed frequency dependence of the variation is in good agreement with the prediction from interstellar scintillation. Adopting a simple model for the annual modulation model and using also the frequency dependence of the IDV, we derive a lower limit to the distance of the scattering screen and an upper limit to the scintillating source size. The latter is found to be consistent with the measured core size from VLBI.

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