arXiv 1202.09262012-02-05astro-ph.SRastro-ph.EP

电子回旋脉塞不稳定性的动力学模拟：有限源尺寸的影响

Kinetic simulation of the electron-cyclotron maser instability: effect of a finite source size

A. A. Kuznetsov, V. G. Vlasov

备注：: Accepted for publication in A&A
DOI：: 10.1051/0004-6361/201118716

摘要：

电子回旋脉塞不稳定性在宇宙中广泛存在，例如，磁化行星和冷的亚恒星物体的无线电发射。诊断天体物理射电源的参数需要对辐射过程进行全面的非线性模拟。我们模拟了极低β等离子体中的电子回旋脉塞不稳定性。所使用的模型考虑了辐射从源区逃逸和粒子流通过该区域。我们开发了一个动力学代码来模拟无线电发射源中电子分布的时间演化。该模型包括描述粒子注入到发射源区域和从发射源区域逃逸的项。通过使用有限的放大时间，从源的发射的空间逃逸被考虑在内。考虑了马蹄型不稳定电子分布。一些模拟进行了不同的参数集典型的行星和超冷矮星的磁层。所产生的发射（对应于基本非寻常模式）具有接近电子回旋频率的频率，并且跨越磁场传播。在模拟开始后不久，电子分布达到准稳态。如果发射源区域相对较小，则所得电子分布与注入电子的分布相似;发射强度较低。在较大的源中，由于波-粒子相互作用，电子分布可能变得几乎平坦，而粒子能量通量到波的转换效率达到10- 20%。我们发现我们的模型与地球和土星极光无线电发射源区域的原位观测结果吻合得很好。得到了超冷矮星磁层中电子分布的预期特征。

英文摘要：

The electron-cyclotron maser instability is widespread in the Universe, producing, e.g., radio emission of the magnetized planets and cool substellar objects. Diagnosing the parameters of astrophysical radio sources requires comprehensive nonlinear simulations of the radiation process. We simulate the electron-cyclotron maser instability in a very low-beta plasma. The model used takes into account the radiation escape from the source region and the particle flow through this region. We developed a kinetic code to simulate the time evolution of an electron distribution in a radio emission source. The model includes the terms describing the particle injection to and escape from the emission source region. The spatial escape of the emission from the source is taken into account by using a finite amplification time. The unstable electron distribution of the horseshoe type is considered. A number of simulations were performed for different parameter sets typical of the magnetospheres of planets and ultracool dwarfs. The generated emission (corresponding to the fundamental extraordinary mode) has a frequency close to the electron cyclotron frequency and propagates across the magnetic field. Shortly after the onset of a simulation, the electron distribution reaches a quasi-stationary state. If the emission source region is relatively small, the resulting electron distribution is similar to that of the injected electrons; the emission intensity is low. In larger sources, the electron distribution may become nearly flat due to the wave-particle interaction, while the conversion efficiency of the particle energy flux into waves reaches 10-20%. We found good agreement of our model with the in situ observations in the source regions of auroral radio emissions of the Earth and Saturn. The expected characteristics of the electron distributions in the magnetospheres of ultracool dwarfs were obtained.

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