X-ray emission provides the most direct diagnostics of the energy-release process in solar flares. Occasionally, a superhot X-ray source is found to be above hot flare loops of ~10 MK temperature. While the origin of the superhot plasma is still elusive, it has conjured up an intriguing image of in-situ plasma heating near the reconnection site high above the flare loops, in contrast to the conventional picture of chromospheric evaporation. Here we investigate an extremely long-duration solar flare, in which EUV images show two distinct flare loop systems that appear successively along a Gamma-shaped polarity inversion line (PIL). When both flare loop systems are present, the HXR spectrum is found to be well fitted by combining a hot component (Te ~12 MK) and a superhot component (Te ~30 MK). Associated with a fast CME, the superhot X-ray source is located at top of the flare arcade that appears earlier, straddling and extending along the long "arm" of the Gamma-shaped PIL. Associated with a slow CME, the hot X-ray source is located at the top of the flare arcade that appears later and sits astride the short "arm" of the Gamma-shaped PIL. Aided by observations from a different viewing angle, we are able to verify that the superhot X-ray source is above the hot one in projection, but the two sources belong to different flare loop systems. Thus, this case study provides a stereoscopic observation explaining the co-existence of superhot and hot X-ray emitting plasmas in solar flares.
A multi-wavelength view of AB Dor's outer atmosphere - Simultaneous X-ray and optical spectroscopy at high cadence
我们研究的色球和日冕的超快旋转AB D或A在高时间和光谱分辨率使用同时观测XMM-牛顿在X射线，VLT/UVES在光学，和ATCA在无线电。我们的光谱具有约50 000的分辨率与时间的节奏约1分钟。我们的观测连续覆盖一个以上的旋转周期，包括静止期和三个不同强度的耀斑事件。从X射线观测中，我们研究了日冕温度、发射量、密度和丰度的变化。我们用循环模型来解释我们的数据。从光学数据中，我们使用耀斑过程中出现的大量发射线来确定耀斑色球物质。详细分析的线条形状和线中心，使我们能够推断的物理特性的耀斑色球层和粗略本地化的耀斑事件的明星。我们特别使用光学高节奏光谱来证明，在第一次耀斑的前十分钟，湍流和斯塔克增宽都存在。此外，在耀斑的最初几分钟，我们在Hα和Ca ii K线中发现了短寿命（一到几分钟）的发射子分量，由于它们的高内禀速度，我们将其解释为与耀斑相关的激波。结合我们的光谱学的结果，基于空间的数据，我们得到耀斑填充因子。最后，比较X射线，光学宽带，线发射，我们发现有两个三个耀斑事件的相关性，而有一个事件没有明确的相关性。此外，我们没有发现无线电数据与任何其他观测数据的任何相关性。
