298颗VLBA校准源的射电成图和结构效应分析

Radio Imaging and Structure Effect Analysis of 298 VLBA Calibrator Sources

为了提高甚长基线阵列(very long baseline array, VLBA)校准射电源位置的精度,建立新一代的国际天球参考架(international celestial reference frame, ICRF),VLBA开展了第二个历元校准源巡天观测(VLBA calibrator survey Ⅱ, VCS-Ⅱ)。BG219I是其中第8组观测,共有298颗射电源在S和X双波段被成功检测到,其中48颗是首次被检测到的射电源。给出了这298颗射电源的成图结果,并根据它们的亮度分布,用δ函数分量建模,计算出这些射电源的结构时延和结构指数。研究了致密度跟结构指数的关系,发现结构指数越小的射电源,具有越大的致密度。还统计了21颗谱指数小于-0.8的陡谱射电源,发现它们在单个波段或者两个波段的结构指数均超过3.0,表明这些射电源不够致密,因而不适合高精度的天体测量。最后,研究了射电源的位置精度与结构指数的关系,发现射电源的位置精度随着结构指数的变大而逐渐降低。

The second epoch very long baseline array(VLBA)calibrator survey campaign(VCS-II)was aimed at improving positional accuracies of phase reference calibrators and establishing the third realization of the international celestial reference frame(ICRF).BG219I,the eighth session of the VCS-II campaign,detected 298 target radio sources at the S/X dual band,of which48sources were newly detected.In this paper,the radio imaging results of the 298 radio sources are presented.According to their brightness distribution,we use delta function components modeling to estimate their structure delays and structure indices,which can be used to judge the astrometric suitability of a radio source.The analysis of“compactness”of 298 radio sources suggested that the radio sources with the smaller structure indices are more compact.We found21steep spectral radio sources with a spectral index less than-0.8,and found that their structure indices at a single band or the both bands are bigger than3.0,which indicate those sources are not so compact and may not be suitable as defining sources of the ICRF.Finally,we counted the positional accuracies of target radio sources.For those sources with smaller structure indices,they have higher positional accuracies.