The Structure and Dynamics of the Subparsec Jet in M87 Based on 50 VLBA Observations over 17 Years at 43GHz
The Structure and Dynamics of the Subparsec Jet in M87 Based on 50 VLBA Observations over 17 Years at 43GHz
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DOI：
10.3847/1538-4357/aaafcc
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发表时间：
2018-03-10
影响因子：
4.9
通讯作者：
Junor, William
中科院分区：
文献类型：
--
作者：
Walker, R. Craig;Hardee, Philip E.;Junor, William
M87的中心射电源提供了研究喷流形成的最佳机会，因为它具有黑洞引力半径的大角度尺寸，并且具有明亮的喷流，可以通过非常长的基线干涉测量观测很好地解决。我们提出了2007年和2008年的密集监测观测，加上大约17年的年度观测，所有观测都是用43 GHz的甚长基线阵列进行的，分辨率约为30 × 60 R（S）。我们的高动态范围图像清楚地显示了大开角结构和反喷流。喷流和反喷流在内部1.5mas（投影为0.12pc）内几乎对称，两者都是边缘增亮的。两者都显示出偏离抛物线形状的形式，即最初的快速膨胀和随后的收缩，随后进一步快速膨胀，并在可见的反喷流之外，随后准直。适当的运动和反喷/喷流强度比都表明从小于或接近0.5c的表观速度到大于或接近2c的加速度，在内部类似于2质量，并建议螺旋流。喷流表现出一个大约8-10年准周期的横向移动。这种转移以非弹道的方式向外传播，并且比移动最快的部件所显示的流速要慢得多。极化数据显示了一个系统的结构与磁场矢量，表明一个环向场接近核心。
The central radio source in M87 provides the best opportunity to study jet formation because it has a large angular size for the gravitational radius of the black hole and has a bright jet that is well resolved by very long baseline interferometry observations. We present intensive monitoring observations from 2007 and 2008, plus roughly annual observations that span 17 years, all made with the the Very Long Baseline Array at 43 GHz with a resolution of about 30 by 60R(S). Our high dynamic range images clearly show the wide opening angle structure and the counterjet. The jet and counterjet are nearly symmetric in the inner 1.5 mas (0.12 pc in projection), with both being edge brightened. Both show deviations from parabolic shape in the form of an initial rapid expansion and subsequent contraction followed by further rapid expansion and, beyond the visible counterjet, subsequent collimation. Proper motions and counterjet/jet intensity ratios both indicate acceleration from apparent speeds of less than or similar to 0.5c to greater than or similar to 2c in the inner similar to 2 mas and suggest a helical flow. The jet displays a sideways shift with an approximately 8-10 yr quasi-periodicity. The shift propagates outward nonballistically and significantly more slowly than the flow speed revealed by the fastest-moving components. Polarization data show a systematic structure with magnetic field vectors that suggest a toroidal field close to the core.