环顶X射线源高密度起源的一个模型
A Model for the Origin of High Density in Loop-top X-ray Sources
摘要：
在一些大的太阳耀斑中探测到的超热环顶源是HXR发射的紧凑源，其光谱与超过30兆开尔文的热电子数相匹配。观测到的高发射测量，以及小源区内电子热化的推断，都提供了环顶高密度的证据;通常比周围环境高出一个数量级以上。有些研究人员提出，这种密度增强的结果从快速增强的磁场强度，我们提出了一个替代模型，Petschek重联的基础上，looptop等离子体加热和压缩的缓慢磁声冲击产生自洽通过磁通量收缩后重联。在稳定的条件下，这种冲击能使密度增加不超过四倍。由于热传导的瞬态效应，这些定常激波关系（Rankine-Hugoniot关系）不适用于Petschek模型。实际上，在整个重联流出过程中，密度的增加可以超过10倍。在不同地点的集合处重新连接后缩回的通量管集合将具有与通量管产生速率成比例的集体发射测量。这个速率不同于单个管内的局部重联速率，可以通过耀斑带运动单独测量。典型的通量传输率和回路参数产生的排放措施，在超热源中观察到的。
英文摘要：
Super-hot looptop sources, detected in some large solar flares, are compact sources of HXR emission with spectra matching thermal electron populations exceeding 30 megakelvins. High observed emission measure, as well as inference of electron thermalization within the small source region, both provide evidence of high densities at the looptop; typically more than an order of magnitude above ambient. Where some investigators have suggested such density enhancement results from a rapid enhancement in the magnetic field strength, we propose an alternative model, based on Petschek reconnection, whereby looptop plasma is heated and compressed by slow magnetosonic shocks generated self-consistently through flux retraction following reconnection. Under steady conditions such shocks can enhance density by no more than a factor of four. These steady shock relations (Rankine-Hugoniot relations) turn out to be inapplicable to Petschek's model owing to transient effects of thermal conduction. The actual density enhancement can in fact exceed a factor of ten over the entire reconnection outflow. An ensemble of flux tubes retracting following reconnection at an ensemble of distinct sites will have a collective emission measure proportional to the rate of flux tube production. This rate, distinct from the local reconnection rate within a single tube, can be measured separately through flare ribbon motion. Typical flux transfer rates and loop parameters yield emission measures comparable to those observed in super-hot sources.
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