太阳耀斑X射线环顶源早期异常温度结构
Early Abnormal Temperature Structure of X-ray Looptop Source of Solar Flares
摘要：
这封信是为了研究一种新发现的现象--在太阳耀斑的早期阶段收缩的耀斑环的物理学。经典的耀斑模型是根据耀斑环的膨胀现象建立的，在耀斑环的上方放置一个能量释放点。这些模型可以预测，由于热传导和冷却效应，耀斑环顶部存在垂直温度梯度。因此，在更高的能量带处的X射线环顶源的质心在高度上将更高，对此我们可以定义为正常温度分布。利用{ \it RHESSI}的观测，我们分析了10个M级或X级耀斑（9个肢体耀斑）。对于所有这些耀斑，环顶源的运动都表现出明显的U型轨迹，我们认为这是耀斑环收缩到膨胀的标志。我们发现，对于所有这些耀斑，正常的温度分布确实存在，但只是沿着膨胀的路径。沿收缩路径的温度分布是不正常的，没有空间秩序。结果表明，这些太阳耀斑在收缩和膨胀阶段的磁重联过程是不同的。
英文摘要：
This Letter is to investigate the physics of a newly discovered phenomenon -- contracting flare loops in the early phase of solar flares. In classical flare models, which were constructed based on the phenomenon of expansion of flare loops, an energy releasing site is put above flare loops. These models can predict that there is a vertical temperature gradient in the top of flare loops due to heat conduction and cooling effects. Therefore, the centroid of an X-ray looptop source at higher energy bands will be higher in altitude, for which we can define as normal temperature distribution. With observations made by {\it RHESSI}, we analyzed 10 M- or X-class flares (9 limb flares). For all these flares, the movement of looptop sources shows an obvious U-shaped trajectory, which we take as the signature of contraction-to-expansion of flare loops. We find that, for all these flares, normal temperature distribution does exist, but only along the path of expansion. The temperature distribution along the path of contraction is abnormal, showing no spatial order at all. The result suggests that magnetic reconnection processes in the contraction and expansion phases of these solar flares are different.
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