STUDIES OF THE JET IN BL LACERTAE. I. RECOLLIMATION SHOCK AND MOVING EMISSION FEATURES
STUDIES OF THE JET IN BL LACERTAE. I. RECOLLIMATION SHOCK AND MOVING EMISSION FEATURES
复制标题
BL Lacetae 中喷射流的研究。
DOI：
10.1088/0004-637x/787/2/151
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
T. Savolainen
中科院分区：
文献类型：
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作者：
M. Cohen;D. Meier;T. Arshakian;T. Arshakian;D. Homan;T. Hovatta;T. Hovatta;Y. Kovalev;Y. Kovalev;M. Lister;A. Pushkarev;A. Pushkarev;J. Richards;T. Savolainen
BL Lac在15 GHz的秒差距尺度VLBA图像显示，射流包含一个永久的准静止发射特征，距离核心0.26 mas（投影0.34 pc），以及许多移动特征。在投影中，运动特征的轨迹以- 166的位置角围绕轴聚集。°6，连接核心与站立功能。运动特征似乎以一种与二维相对论磁流体动力学（RMHD）数值模拟结果惊人相似的方式从站立特征中发出，其中运动冲击是在再准直冲击（RCS）中产生的。由于这一点，以及与M87中的射流特征HST-1的相似之处，我们将BL Lac中的静止特征确定为RCS。我们假设磁场主导着射流的动力学，并且磁场主要是环形的。由此，我们认为运动特征是由慢速和快速磁声MHD波建立的压缩。我们用一个简单的模型来说明这种情况，其中最慢的运动特征是慢模波，最快的运动特征是快模波。在该模型中，光束在宿主星系的框架中具有洛伦兹因子，快模波在光束的框架中具有洛伦兹因子。这给出了移动特征的最大表观速度，βapp = vapp/c = 10。在这个模型中，星系框架中图案的洛伦兹因子大约是光束本身的三倍。
Parsec-scale VLBA images of BL Lac at 15 GHz show that the jet contains a permanent quasi-stationary emission feature 0.26 mas (0.34 pc projected) from the core, along with numerous moving features. In projection, the tracks of the moving features cluster around an axis at a position angle of −166.°6 that connects the core with the standing feature. The moving features appear to emanate from the standing feature in a manner strikingly similar to the results of numerical two-dimensional relativistic magneto-hydrodynamic (RMHD) simulations in which moving shocks are generated at a recollimation shock (RCS). Because of this, and the close analogy to the jet feature HST-1 in M87, we identify the standing feature in BL Lac as an RCS. We assume that the magnetic field dominates the dynamics in the jet, and that the field is predominantly toroidal. From this we suggest that the moving features are compressions established by slow and fast mode magneto-acoustic MHD waves. We illustrate the situation with a simple model in which the slowest moving feature is a slow-mode wave, and the fastest feature is a fast-mode wave. In the model, the beam has Lorentz factor in the frame of the host galaxy and the fast mode wave has Lorentz factor in the frame of the beam. This gives a maximum apparent speed for the moving features, βapp = vapp/c = 10. In this model the Lorentz factor of the pattern in the galaxy frame is approximately three times larger than that of the beam itself.