KVN观测值的振幅修正因子
Amplitude Correction Factors of KVN Observations
摘要：
本文报道了韩国VLBI观测网（KVN）甚长基线干涉测量（VLBI）振幅定标的研究结果。利用韩国天文空间科学研究所（KASI）大田硬件相关器和DiFX软件相关器的22 GHz KVN观测数据与韩国国家射电天文台（NRAO）DiFX软件相关器的22 GHz甚长基线天线阵（VLBA）观测数据进行对比，估算了振幅校正因子。我们使用了致密射电源3C 454.3、NRAO 512、OJ 287、BL Lac、3C 279、1633+382和1510-089的观测结果，这些观测结果在350-477 km的基线范围内几乎无法分辨。选择在KVN和VLBA上用相似基线获得的源的可见度数据，进行条纹拟合、校准，并比较它们的振幅。我们发现，KVN观测的可见度振幅应分别由1.10和1.35的因子进行校正，与DiFX和大田修正因子相关。这些校正因子是由于KVN观测系统中两步2比特量化和大田相关器的特性相结合而产生的。
英文摘要：
We report results of investigation of amplitude calibration for very long baseline interferometry (VLBI) observations with Korean VLBI Network (KVN). Amplitude correction factors are estimated based on comparison of KVN observations at 22~GHz correlated by Daejeon hardware correlator and DiFX software correlator in Korea Astronomy and Space Science Institute (KASI) with Very Long Baseline Array (VLBA) observations at 22~GHz by DiFX software correlator in National Radio Astronomy Observatory (NRAO). We used the observations for compact radio sources, 3C 454.3, NRAO 512, OJ 287, BL Lac, 3C 279, 1633+382, and 1510-089, which are almost unresolved for baselines in a range of 350-477 km. Visibility data of the sources obtained with similar baselines at KVN and VLBA are selected, fringe-fitted, calibrated, and compared for their amplitudes. We found that visibility amplitudes of KVN observations should be corrected by factors of 1.10 and 1.35 when correlated by DiFX and Daejeon correlators, respectively. These correction factors are attributed to the combination of two steps of 2-bit quantization in KVN observing systems and characteristics of Daejeon correlator.
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