arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1404.0976astro-ph.HEastro-ph.COastro-ph.GA
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BL蜥蜴类喷流的研究I.再准直激波和运动辐射特征

Studies of the Jet in BL Lacertae I. Recollimation Shock and Moving Emission Features

M. H. Cohen, D. L. Meier, T. G. Arshakian, D. C. Homan, T. Hovatta, Y. Y. Kovalev, M. L. Lister, A. B. Pushkarev, J. L. Richards, T. Savolainen

摘要:

在15 GHz的BL Lac的秒差距尺度VLBA图像显示,射流包含一个永久的准静态发射功能0.26 mas(0.34 pc投影)从核心,以及许多移动功能。在投影中,移动特征的轨迹以位置角-166.6度围绕连接核心与站立特征的轴聚集。移动的功能似乎从常设功能的方式惊人地相似的数值2-D相对论磁流体动力学(RMHD)模拟的结果,其中移动的冲击产生在校准冲击。由于这一点,以及与M87中的喷流特征HST-1的密切类比,我们将BL Lac中的静止特征确定为一个准平激波。我们假设,磁场占主导地位的动力学在射流中,该领域是占主导地位的环形。由此,我们认为,移动的功能是由慢模式和快模式磁声MHD波建立的压缩。我们用一个简单的模型来说明这种情况,在这个模型中,最慢的移动特征是慢模式波,而最快的特征是快模式波。在该模型中,光束在宿主星系系中的洛伦兹因子约为3.5,快模波在光束系中的洛伦兹因子约为1.6。这给出了移动特征10 c的最大视在速度。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3倍。

英文摘要:

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 position angle -166.6 deg 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 2-D relativistic magneto-hydrodynamic (RMHD) simulations in which moving shocks are generated at a recollimation shock. Because of this, and the close analogy to the jet feature HST-1 in M87, we identify the standing feature in BL Lac as a recollimation shock. 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 about 3.5 in the frame of the host galaxy, and the fast mode wave has Lorentz factor about 1.6 in the frame of the beam. This gives a maximum apparent speed for the moving features 10c. In this model the Lorentz factor of the pattern in the galaxy frame is approximately 3 times larger than that of the beam itself.

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