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arXiv 2101.06962astro-ph.HE
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大尺度磁场结构相对论喷流中喷出物的通量变化

Flux variability from ejectas in structured relativistic jets with large-scale magnetic fields

Gaëtan Fichet de Clairfontaine, Zakaria Meliani, Andreas Zech, Olivier Hervet

摘要:

利用相对论MHD程序MPI-AMRVAC和后处理程序中的辐射转移程序,我们研究了磁场位形和超压射流的横向分层对其形态、运动激波动力学和发射射电光变曲线的影响。首先,我们研究了不同的大尺度磁场对驻激波和分层射流形态的影响。其次,我们研究了运动激波与驻激波的相互作用。我们计算合成同步辐射图和射电光变曲线,并分析在两个频率1和15.3 GHz和几个观测角度的变化。最后,我们比较了我们模拟的光变曲线与2008年至2019年MOJAVE调查中使用OVRO和VLBA从blazar 3C 273观测到的射电耀斑的特征。我们发现,在一个结构化的,超压的相对论性喷流中,大尺度磁场结构的存在改变了驻激波的性质,并导致射流的开放。当穿越这样的驻激波时,伴随着注入喷流底部的高密度的运动激波会引起非常明亮的射电耀斑。在不同视角下对这些耀斑的时间结构的观测探测了不同光学深度的喷流。在1 GHz和小角度下,由移动冲击波引起的自吸收变得更加重要,并导致在与最亮的站立结相互作用后观察到的通量下降。一个弱的不对称性被认为是在模拟耀斑的形状,从剩余的发射的冲击立激波。模拟耀斑的特性和光变曲线中的峰值与移动激波和立激波的交叉的相关性有利于这种情况作为对3C 273观测到的射电耀斑的解释。

英文摘要:

Using the relativistic MHD code MPI-AMRVAC and a radiative transfer code in post-processing, we explore the influence of the magnetic-field configuration and transverse stratification of an over-pressured jet on its morphology, on the moving shock dynamics, and on the emitted radio light curve. First, we investigate different large-scale magnetic fields with their effects on the standing shocks and on the stratified jet morphology. Secondly, we study the interaction of a moving shock wave with the standing shocks. We calculate the synthetic synchrotron maps and radio light curves and analyse the variability at two frequencies 1 and 15.3 GHz and for several observation angles. Finally, we compare the characteristics of our simulated light curves with radio flares observed from the blazar 3C 273 with OVRO and VLBA in the MOJAVE survey between 2008 and 2019. We find that, in a structured, over-pressured relativistic jet, the presence of the large-scale magnetic field structure changes the properties of the standing shock waves and leads to an opening of the jet. When crossing such standing shocks, moving shock waves accompanying overdensities injected in the base of the jet are causing very luminous radio flares. The observation of the temporal structure of these flares under different viewing angles probes the jet at different optical depths. At 1 GHz and for small angles, the self-absorption caused by the moving shock wave becomes more important and leads to a drop in the observed flux after it interacts with the brightest standing knot. A weak asymmetry is seen in the shape of the simulated flares, resulting from the remnant emission of the shocked standing shocks. The characteristics of the simulated flares and the correlation of peaks in the light curve with the crossing of moving and standing shocks favor this scenario as an explanation of the observed radio flares of 3C 273.

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