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arXiv 2302.00451astro-ph.SR
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微波对等离子体平板扭折振荡的响应

Microwave response to kink oscillations of a plasma slab

T. I. Kaltman, E. G. Kupriyanova

摘要:

研究了线性扭折快磁声波对等离子体板微波辐射强度的调制。板片沿直的磁场伸展,并且可以表示例如太阳日冕中的耀斑活动区域中的电流片,或者流光或伪流光柄。等离子体密度在垂直方向上是不均匀的,并由对称的爱泼斯坦轮廓描述。等离子体参数$β$取为零,这是一个很好的近似太阳日冕活动区。微波辐射是由温和的相对论电子占据振荡板内的一层,并通过回旋同步加速器(GS)机制辐射。在GS光谱的光学薄部分模拟了微波发射的光变曲线,并分析了它们的典型傅里叶光谱。结果表明,微波对线性扭折磁流体动力学波的响应是非线性的。结果表明,当波节处的微波光变曲线以与扰动扭折模相同的频率振荡时,波腹处的微波振荡频率是扭折振荡频率的两倍。当从节点滑动到反节点时,发生从一种类型的光变曲线到另一种类型的光变曲线的逐渐变换。该结果不依赖于振荡板内部的GS发射层的宽度。这一发现应被视为在太阳和恒星耀斑的微波准周期脉动的解释。

英文摘要:

The modulation of the intensity of microwave emission from a plasma slab caused by a standing linear kink fast magnetoacoustic wave is considered. The slab is stretched along a straight magnetic field, and can represent, for example, a current sheet in a flaring active region in corona of the Sun, or a streamer or pseudostreamer stalk. The plasma density is non-uniform in the perpendicular direction and described by a symmetric Epstein profile. The plasma parameter $β$ is taken to be zero, which is a good approximation for solar coronal active regions. The microwave emission is caused by mildly relativistic electrons which occupy a layer within the oscillating slab and radiate via the gyrosynchrotron (GS) mechanism. Light curves of the microwave emission were simulated in the optically thin part of the GS spectrum, and their typical Fourier spectra were analysed. It is shown that the microwave response to a linear kink magnetohydrodynamic wave is non-linear. It is found that, while the microwave light curves at the node oscillate with the same frequency as the frequency of the perturbing kink mode, the frequency of the microwave oscillations at the anti-node is two times higher than the kink oscillation frequency. Gradual transformation the one type of the light curves to another occurs when sliding from the node to the anti-node. This result does not depend on the width of the GS-emitting layer inside the oscillating slab. This finding should be considered in the interpretation of microwave quasi-periodic pulsations in solar and stellar flares.

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