THEORY OF GYRORESONANCE AND FREE–FREE EMISSIONS FROM NON-MAXWELLIAN QUASI-STEADY-STATE ELECTRON DISTRIBUTIONS
THEORY OF GYRORESONANCE AND FREE–FREE EMISSIONS FROM NON-MAXWELLIAN QUASI-STEADY-STATE ELECTRON DISTRIBUTIONS
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非麦克斯韦准稳态电子分布的陀螺谐振理论和自由-自由发射
DOI：
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发表时间：
2013
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通讯作者：
A. Kuznetsov
中科院分区：
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作者：
G. Fleishman;A. Kuznetsov
目前，人们担心经典热（麦克斯韦）分布描述太阳大气中准稳态等离子体（包括活动区域）的能力。特别是，为了更好地拟合观测值，人们提出了其他分布，例如 kappa 分布和 n 分布。如果存在，这些分布将产生与经典陀螺谐振（GR）或自由-自由发射相比具有不同可观测特性的无线电发射，这意味着在无线电观测中远程检测这些非麦克斯韦分布的方法。在这里，我们提出了通过分析得出的 GR 和自由-自由发射率以及 kappa 和 n 分布的吸收系数，并讨论了它们的性质，它们实际上彼此之间以及与经典麦克斯韦等离子体有显着的不同。特别是，对于 kappa 分布，陀螺层的射电亮度温度随光学深度 τ 增加而增加，但对于 n 分布则随着 τ 减少。这一特性具有显着的结果，允许进行直接的观测测试：即使在光学厚的情况下，来自非麦克斯韦分布的GR射电发射也应该具有明显的偏振，而在麦克斯韦等离子体的情况下，发射将具有严格的零偏振。这提供了一种远程探测天体物理源中等离子体分布的方法，包括太阳活动区域作为一个生动的例子。
Currently there is a concern about the ability of the classical thermal (Maxwellian) distribution to describe quasi-steady-state plasma in the solar atmosphere, including active regions. In particular, other distributions have been proposed to better fit observations, for example, kappa- and n-distributions. If present, these distributions will generate radio emissions with different observable properties compared with the classical gyroresonance (GR) or free–free emission, which implies a way of remotely detecting these non-Maxwellian distributions in the radio observations. Here we present analytically derived GR and free–free emissivities and absorption coefficients for the kappa- and n-distributions, and discuss their properties, which are in fact remarkably different from each other and from the classical Maxwellian plasma. In particular, the radio brightness temperature from a gyrolayer increases with the optical depth τ for kappa-distribution, but decreases with τ for n-distribution. This property has a remarkable consequence allowing a straightforward observational test: the GR radio emission from the non-Maxwellian distributions is supposed to be noticeably polarized even in the optically thick case, where the emission would have strictly zero polarization in the case of Maxwellian plasma. This offers a way of remote probing the plasma distribution in astrophysical sources, including solar active regions as a vivid example.