天鹅座A原始热点非热粒子的最大能量
On the maximum energy of non-thermal particles in the primary hotspot of Cygnus A
摘要：
本文研究了射电星系天鹅座A西北急流中主要热点的粒子加速和磁场放大。通过使用在43 GHz的一个很好地解决了这个热点的区域中所观察到的磁通密度，我们确定的射流密度的最小值和约束的磁场的大小。我们发现，一个喷流的密度大于$5\times 10^{-5}$ cm $^{-3}$和热点磁场在50 - 400 $μ$ G的范围内需要解释同步辐射在43 GHz。热点同步辐射谱的能量上限截止频率<$5\times 10^{14}$ Hz，表明在磁场为100 $μ$ G时，喷流反向激波加速的非热电子的最大能量为$E_{e, \rm max} \sim 0.8$ TeV。基于磁湍流尺度长度必须大于等离子体趋肤深度的条件，以及非热粒子的能量密度不能违反射流动力学光度所施加的限制，我们证明了$E_{e,\rm max}$不能像传统假设的那样受到同步辐射损失的约束。除此之外，并假设冲击是准垂直的，我们表明，非共振混合不稳定性产生的宇宙射线流与能量$E_{e, \rm max}$可以增长得足够快，以放大喷流磁场高达50 - 400 $μ$ G和加速粒子的最大能量$E_{e, \rm max}$在天鹅座A的主要热点。
英文摘要：
We study particle acceleration and magnetic field amplification in the primary hotspot in the northwest jet of radiogalaxy Cygnus A. By using the observed flux density at 43 GHz in a well resolved region of this hotspot, we determine the minimum value of the jet density and constrain the magnitude of the magnetic field. We find that a jet with density greater than $5\times 10^{-5}$ cm$^{-3}$ and hotspot magnetic field in the range 50-400 $μ$G are required to explain the synchrotron emission at 43 GHz. The upper-energy cut-off in the hotspot synchrotron spectrum is at a frequency < $5\times 10^{14}$ Hz, indicating that the maximum energy of non-thermal electrons accelerated at the jet reverse shock is $E_{e, \rm max} \sim 0.8$ TeV in a magnetic field of 100 $μ$G. Based on the condition that the magnetic-turbulence scale length has to be larger than the plasma skin depth, and that the energy density in non-thermal particles cannot violate the limit imposed by the jet kinetic luminosity, we show that $E_{e,\rm max}$ cannot be constrained by synchrotron losses as traditionally assumed. In addition to that, and assuming that the shock is quasi-perpendicular, we show that non-resonant hybrid instabilities generated by the streaming of cosmic rays with energy $E_{e, \rm max}$ can grow fast enough to amplify the jet magnetic field up to 50-400 $μ$G and accelerate particles up to the maximum energy $E_{e, \rm max}$ observed in the Cygnus A primary hotspot.
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