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arXiv 1402.0853astro-ph.HEastro-ph.GA
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天鹅座A射电腔同步辐射的首次动力学计算腔中存在电子对等离子体的证据

First Dynamic Computation of Synchrotron Emission from the Cygnus A Radio Cavity; Evidence for Electron Pair Plasma in Cavity

William G. Mathews

摘要:

宇宙射线,热气体和磁场在FRII无线电腔被假定完全来自风流动从后面的喷流冲击。结合分析和计算的方法,它表明,计算的无线电电子能量分布和同步辐射发射率光谱无处不在的天鹅座A无线电腔同意与无线电观测的天鹅座A瓣。磁场的能量密度在各处都很小,并且在冲击后的风中被动地演化。大多数同步辐射产生于最近的激波后物质,因为它沿着无线电腔壁回流。因为它经历了较少的绝热膨胀,这个年轻的回流中的磁场比射电瓣中的其他地方更大,解释了观测到的射电同步加速器边缘增亮。边界回流减速,由于小腔压力梯度,导致大规模的领域垂直于回流(和同步辐射),以指数增长不同于观察。然而,如果该领域是随机的亚网格(次千秒差距)尺度上,计算场再现的幅度和缓慢下降的无线电同步辐射沿回流观察到的发射率。用小尺度随机场计算的射电同步辐射谱和图象与VLA观测结果一致。计算使射电腔膨胀所需的喷流后激波区的总相对论性能量密度与在天鹅座A激波后区观察到的相对论性电子的能量密度相匹配。这表明在喷流和空腔中控制动力学演化的成分是相对论对等离子体。

英文摘要:

Cosmic rays, thermal gas and magnetic fields in FRII radio cavities are assumed to come entirely from winds flowing from just behind the jet shocks. Combining analytic and computational methods, it is shown that the computed radio-electron energy distribution and synchrotron emissivity spectra everywhere in the Cygnus A radio cavity agrees with radio observations of the Cygnus A lobes. The magnetic field energy density is small everywhere and evolves passively in the post-shock wind. Most synchrotron emission arises in recent post-shock material as it flows back along the radio cavity wall. Because it experienced less adiabatic expansion, the magnetic field in this young backflow is larger than elsewhere in the radio lobe, explaining the observed radio synchrotron limb-brightening. The boundary backflow decelerates due to small cavity pressure gradients, causing large-scale fields perpendicular to the backflow (and synchrotron emission) to grow exponentially unlike observations. However, if the field is random on subgrid (sub-kpc) scales, the computed field reproduces both the magnitude and slowly decreasing radio synchrotron emissivity observed along the backflow. The radio synchrotron spectrum and image computed with a small-scale random field agree with VLA observations. The total relativistic energy density in the post-jet shock region required in computations to inflate the radio cavity matches the energy density of relativistic electrons observed in the post-shock region of Cygnus A. This indicates that the component in the jet and cavity that dominates the dynamical evolution is a relativistic pair plasma.

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