用扭曲纤维模拟M87内射流
Using Twisted Filaments to Model the Inner Jet in M87
摘要：
M87喷流的无线电和光学图像显示出明亮的细丝，扭曲成明显的双螺旋，从HST-1延伸到结A。喷流内部的适当运动表明减速喷流穿过较慢的加速波型。我们使用这些观测结果来开发一个质量和能量通量守恒模型，描述射流和沿射流的条件。我们确定的茧条件所需的扭曲的长丝是开尔文-亥姆霍兹（KH）不稳定的椭圆模式的结果。我们发现，在HST-1处，茧的温度一定比射流的温度低，但温度一定与结点A处的射流的温度差不多。在这些条件下，我们发现，所观察到的灯丝波长接近椭圆模式的最大增长率和增长是足够快的灯丝发展和饱和之前HST-1。我们产生一个伪同步图像的模型射流进行正常模式的KH不稳定性的组合。喷流的伪同步加速器图像揭示：（1）模型喷流表面亮度的缓慢下降仍然比真实喷流快约5倍;（2）如果对喷流的螺旋扰动很小或在结A内不存在，KH产生的双螺旋扭曲细丝可以定性地出现在真实喷流上;（3）真实喷流中的结与扭曲的边界特征无关，也不可能是KH不稳定性的结果。真实喷流中的结的存在、无线电中真实喷流的临边增亮以及真实喷流表面亮度的缓慢下降表明喷流内部正在发生额外的过程，如不稳定喷流和内部粒子加速。KH不稳定性对结A以外的真实射流的破坏与我们在结A处发现的射流和茧的条件是一致的。
英文摘要：
Radio and optical images of the M87 jet show bright filaments, twisted into an apparent double helix, extending from HST-1 to knot A. Proper motions within the jet suggest a decelerating jet flow passing through a slower, accelerating wave pattern. We use these observations to develop a mass and energy flux conserving model describing the jet flow and conditions along the jet. We determine the cocoon conditions required if the twisted filaments are the result of the Kelvin-Helmholtz (KH) unstable elliptical mode. We find that the cocoon must be cooler than the jet at HST-1 but must be about as hot as the jet at knot A. Under these conditions we find that the observed filament wavelength is near the elliptical mode maximum growth rate and growth is rapid enough for the filaments to develop and saturate well before HST-1. We generate a pseudo-synchrotron image of a model jet carrying a combination of normal modes of the KH instability. The pseudo-synchrotron image of the jet reveals: (1) that a slow decline in the model jet's surface brightness is still about five times faster than the real jet; (2) that KH produced dual helically twisted filaments can appear qualitatively similar to those on the real jet if any helical perturbation to the jet is very small or nonexistent inside knot A; (3) that the knots in the real jet cannot be associated with the twisted filamentary features and are unlikely to be the result of a KH instability. The existence of the knots in the real jet, the limb brightening of the real jet in the radio, and the slower decline of the surface brightness of the real jet indicate that additional processes --- such as unsteady jet flow and internal particle acceleration --- are occurring within the jet. Disruption of the real jet beyond knot A by KH instability is consistent with the jet and cocoon conditions we find at knot A.
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