Collisionless Reconnection and High-Energy Particle Acceleration in Solar Flares
Collisionless Reconnection and High-Energy Particle Acceleration in Solar Flares
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DOI：
10.1086/304449
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发表时间：
1997-08
期刊：
影响因子：
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通讯作者：
B. Somov;T. Kosugi
中科院分区：
文献类型：
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作者：
B. Somov;T. Kosugi
使用Yohkoh上的硬X射线望远镜（HXT）和软X射线望远镜（SXT）进行的观测表明，重联过程对于脉冲和渐进耀斑是常见的。我们适用于碰撞重联理论，更准确地说，模型的高温超导电流片（HTTCS）的日冕条件来自Yohkoh数据的网站和机制的磁能转化为动能和热能的“超热”等离子体和加速粒子。我们认为重联电流片是耀斑能量的来源，也是电子和离子两步加速到高能的第一步机制。根据我们的模型，重新连接的磁力线迅速移出HTTCS，被冻结成超热等离子体，并在位于强磁场软X射线发射环上方的快速斜无碰撞激波（FOCS）的上游侧形成磁环。由HTTCS激励和预加速的电子和离子被捕获在磁环中。每个环的顶部以高速向FOCS移动，而它的脚穿透激波阵面。由于这些原因，有两种机制塌缩陷阱内部的绝热加热和陷阱两英尺处激波前沿的加速有效地增加了粒子能量。单个坍缩陷阱的寿命可以通过观察到的硬X射线和伽马射线发射到更高能量的几秒钟延迟来确定。加速电子的陷阱可以被看作是日冕硬X射线的“环顶以上源”。加速电子从陷阱通过FOCS进入色球层的沉淀是硬X射线“足点源”的原因。该模型解释了太阳耀斑中硬X射线源的时间、位置和运动，以及观测到的日冕和色球硬X射线源的相对强度和其他物理特性。
Observations with the Hard X-Ray Telescope (HXT) and the Soft X-Ray Telescope (SXT) on board Yohkoh show that the reconnection process is common to impulsive and gradual flares. We apply the collisionless reconnection theory—more exactly, the model of a high-temperature turbulent-current sheet (HTTCS)—to the coronal conditions derived from the Yohkoh data on the site and mechanism of magnetic energy transformation into kinetic and thermal energies of “superhot” plasma and accelerated particles. We consider the reconnecting current sheet as the source of flare energy and the first-step mechanism in a two-step acceleration of electrons and ions to high energies. According to our model, reconnected field lines rapidly move out of the HTTCS, being frozen into superhot plasma, and form magnetic loops on the upstream side of a fast oblique collisionless shock (FOCS) situated above the soft X-ray-emitting loops of a strong magnetic field. The electrons and ions energized and preaccelerated by the HTTCS are trapped in magnetic loops. The top of each loop moves with a high speed toward the FOCS, while its feet penetrate through the shock front. For these reasons, two mechanisms—the adiabatic heating inside the collapsing trap and acceleration by the shock front at the two feet of the trap—efficiently increase the particle energy. The lifetime of an individual collapsing trap can be identified with the observed few-second delay to higher energies of hard X-ray and gamma-ray emission. The trap of accelerated electrons can be seen as the coronal hard X-ray “above-the-loop-top source.” Precipitation of accelerated electrons from the trap through the FOCS into the chromosphere is responsible for the hard X-ray “footpoint sources.” The model explains timing, location, and motion of the hard X-ray sources in solar flares as well as the observed relative intensity of the coronal and chromospheric hard X-ray sources and other physical properties.