Blazar spectral variability as explained by a twisted inhomogeneous jet
Blazar spectral variability as explained by a twisted inhomogeneous jet
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DOI：
10.1038/nature24623
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发表时间：
2017-12
期刊：
影响因子：
64.8
通讯作者：
C. Raiteri;M. Villata;J. Acosta-Pulido;I. Agudo;A. Arkharov;R. Bachev;G. V. Baida;E. Benítez-
中科院分区：
文献类型：
--
作者：
C. Raiteri;M. Villata;J. Acosta-Pulido;I. Agudo;A. Arkharov;R. Bachev;G. V. Baida;E. Benítez-
耀变体是活动星系核，是强大的辐射源，其中心引擎位于宿主星系的核心。Blazar的辐射主要是来自喷流的非热辐射，喷流以相对论的方式向我们移动，因此会发生多普勒波束。这种光束导致通量增强和可变时间尺度的收缩，因此大多数耀变体看起来像是发光的光源，其特征是在所有频率下亮度都有明显和快速的变化。产生这种不可预测的可变性的机制正在辩论中，但提出的机制包括粒子的注入，加速和冷却，以及可能的冲击波或湍流的干预。观测到的发射结或喷流区域的视角变化也被认为是耀斑事件的一种解释，也可以解释耀变体发射的特定性质，如日内变化，准周期性，以及相对于光学变化的无线电通量变化的延迟。然而，这种几何解释并没有被普遍接受，因为基于物理条件变化的其他解释，如发射区的大小和速度，磁场，发射粒子的数量及其能量分布，可以解释在许多情况下耀变体光谱行为的快照。在这里，我们报告的结果的光学到无线电波长监测的耀变体CTA 102，并表明，所观察到的长期趋势的流量和光谱的变化是最好的解释了一个不均匀的，弯曲的喷流，随着时间的推移，经历了方向的变化。我们建议，磁流体动力学不稳定性或旋转的扭曲射流导致不同的射流区域，以改变它们的方向，因此它们的相对多普勒因子。特别是，2016-2017年的极端光学爆发（亮度增加6个星等）发生在相应的发射区域具有小视角时。观测结果与理论预测的一致性可以被看作是相对论性聚束理论的进一步验证。
Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming. This beaming causes flux enhancement and contraction of the variability timescales, so that most blazars appear as luminous sources characterized by noticeable and fast changes in brightness at all frequencies. The mechanism that produces this unpredictable variability is under debate, but proposed mechanisms include injection, acceleration and cooling of particles, with possible intervention of shock waves,or turbulence. Changes in the viewing angle of the observed emitting knots or jet regions have also been suggested as an explanation of flaring events,,,,and can also explain specific properties of blazar emission, such as intra-day variability, quasi-periodicity,and the delay of radio flux variations relative to optical changes. Such a geometric interpretation, however, is not universally accepted because alternative explanations based on changes in physical conditions—such as the size and speed of the emitting zone, the magnetic field, the number of emitting particles and their energy distribution—can explain snapshots of the spectral behaviour of blazars in many cases,. Here we report the results of optical-to-radio-wavelength monitoring of the blazar CTA 102 and show that the observed long-term trends of the flux and spectral variability are best explained by an inhomogeneous, curved jet that undergoes changes in orientation over time. We propose that magnetohydrodynamic instabilities or rotation of the twisted jet cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the extreme optical outburst of 2016–2017 (brightness increase of six magnitudes) occurred when the corresponding emitting region had a small viewing angle. The agreement between observations and theoretical predictions can be seen as further validation of the relativistic beaming theory.