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arXiv 1302.2860astro-ph.SRastro-ph.HE
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X射线太阳耀斑环的时间变化：长度、充实度、位置、温度、等离子体压力和光谱

Temporal variations of X-ray solar flare loops: length, corpulence, position, temperature, plasma pressure and spectra

Natasha L. S. Jeffrey, Eduard P. Kontar

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摘要：

本文研究了三次太阳耀斑日冕X射线环在X射线峰值发射前、发射中和发射后的空间和光谱特性。利用Ramaty高能太阳光谱成像仪（RHESSI）的观测资料，推导出发射X射线的长度、体积、位置、数密度和热压力随时间的变化。我们观察到在X射线峰之前环的长度、宽度和体积减小，并且数密度和热压增加。在X射线峰值之后，体积增加，并且由于宽度增加而使袢肥大。体积变化比位置变化更明显，通常称为磁力线收缩。我们相信这是第一次专门研究X射线环长度和宽度的时间演变。总的来说，观测还首次显示了由温度、X射线发射和热压峰值给出的三个时间阶段，最小体积与X射线峰值一致。虽然在X射线发射的峰值之前，燃烧的等离子体的体积减小，但温度与体积之间的关系不支持塌陷磁阱模型中的简单压缩加热。在低β等离子体中，垂直于引导场的收缩环宽度可以通过挤压穿过该区域的磁场来解释。等离子体加热导致色球蒸发和数密度增加，产生增加的热压力和减少的环长度，因为电子在较短的距离上相互作用，我们相信在X射线峰值之后，环的增大。

英文摘要：

The spatial and spectral properties of three solar flare coronal X-ray loops are studied before, during and after the peak X-ray emission. Using observations from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we deduce the temporal changes in emitting X-ray length, corpulence, volume, position, number density and thermal pressure. We observe a decrease in the loop length, width and volume before the X-ray peak, and an increasing number density and thermal pressure. After the X-ray peak, volume increases and loop corpulence grows due to an increasing width. The volume variations are more pronounced than the position variations, often known as magnetic line contraction. We believe this is the first dedicated study of the temporal evolution of X-ray loop lengths and widths. Collectively, the observations also show for the first time three temporal phases given by peaks in temperature, X-ray emission and thermal pressure, with minimum volume coinciding with the X-ray peak. Although the volume of the flaring plasma decreases before the peak in X-ray emission, the relationship between temperature and volume does not support simple compressive heating in a collapsing magnetic trap model. Within a low beta plasma, shrinking loop widths perpendicular to the guiding field can be explained by squeezing the magnetic field threading the region. Plasma heating leads to chromospheric evaporation and growing number density, producing increasing thermal pressure and decreasing loop lengths as electrons interact at shorter distances and we believe after the X-ray peak, the increasing loop corpulence.

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