Magnetic field strength and spectral distribution of six parsec-scale active galactic nuclei jets
Magnetic field strength and spectral distribution of six parsec-scale active galactic nuclei jets
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DOI：
10.1111/j.1365-2966.2009.15428.x
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发表时间：
2009-07
影响因子：
4.8
通讯作者：
S. O’Sullivan;D. Gabuzda
中科院分区：
文献类型：
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作者：
S. O’Sullivan;D. Gabuzda
我们利用8个频率(4.6、5.1、7.9、8.9、12.9、15.4、22.2和43.1 GHz)的超长基线阵列(VLBA)观测到的6颗“blazar”星，研究了它们的VLBI核心的频率依赖位置(‘芯移’)和它们的整体喷流谱分布。通过对光学薄喷流发射的相互关联，我们能够精确地对齐三个喷流(1418+546,2007+777,2200+420)的多频图像，我们发现它们的芯移和频谱符合Blandford&Konigl锥形喷流模型的均分制度，其中射电核从喷流底部的位置遵循r核的位置(对于0954+658的喷流，我们使用我们的低频测量对齐了高频图像，假设射电核在4.6-43 GHz之间均分)。我们样本中其他两个源(1156+295,1749+096)的喷流发射太稀疏，我们的对准技术无法工作。利用我们测量的核心位移，我们计算了这四个活动星系核在4.6-13 GHz的射电核心中10秒到100秒量级的等分磁场强度。将我们的结果外推到吸积盘和黑洞喷流发射距离，我们发现磁场强度与磁力喷流理论模型的预期一致。
We use observations of six 'blazars' with the Very Long Baseline Array (VLBA), at eight frequencies (4.6, 5.1, 7.9, 8.9, 12.9, 15.4, 22.2 and 43.1 GHz), to investigate the frequency-dependent position of their VLBI cores ('core-shift') and their overall jet spectral distribution. By cross-correlating the optically thin jet emission, we are able to accurately align the multifrequency images of three of the jets (1418+546, 2007+777, 2200+420), whose core-shifts and spectra we find consistent with the equipartition regime of the Blandford & Konigl conical jet model, where the position of the radio core from the base of the jet follows r core (ν) ∝ ν ―1 For the jet of 0954+658, we align the higher frequency images using our lower frequency measurements assuming equipartition in the radio core from 4.6―43 GHz. The jet emission of the other two sources in our sample (1156+295, 1749+096) is too sparse for our alignment technique to work. Using our measured core-shifts, we calculate equipartition magnetic field strengths of the order of 10s to 100s of mG in the radio cores of these four AGN from 4.6―13 GHz. Extrapolating our results back to the accretion disc and black hole jet-launching distances, we find magnetic field strengths consistent with those expected from theoretical models of magnetically powered jets.