BEAMING OF PARTICLES AND SYNCHROTRON RADIATION IN RELATIVISTIC MAGNETIC RECONNECTION
BEAMING OF PARTICLES AND SYNCHROTRON RADIATION IN RELATIVISTIC MAGNETIC RECONNECTION
复制标题
相对论磁重联中的粒子束和同步辐射
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
T. Piran
中科院分区：
文献类型：
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作者：
D. Kagan;E. Nakar;T. Piran
相对论性重联在许多天体物理系统中被用作粒子加速的机制。根据理想化的分析模型，重联产生了大量的相对论流出新兴的重联网站（X点）。因此，产生的辐射是高度集中的。使用二维粒子细胞模拟，我们调查粒子和辐射光束，发现一个非常不同的图片。我们发现，在X点上粒子的整体运动与它们的洛伦兹因子γ相似，而不是在其静止坐标系中具有各向同性电子速度分布的相对论平均整体运动。在从X点到磁岛的过程中，粒子在磁场中转动，形成一个局限于电流片的扇形。一旦它们到达岛屿，它们在完成一个完整的拉莫尔回转后就各向同性化了，它们的辐射不再强烈。给定频率下的辐射图案取决于相应的发射电子辐射其能量的位置。缓慢冷却的低能粒子大部分时间都在岛上度过，它们的辐射并不强烈。只有在X点边缘快速冷却的粒子才会产生高度光束化的扇形辐射图案。从这些快速冷却的粒子中出现的辐射高于燃尽极限（在重新连接的等离子体的整个静止框架中为100 MeV）。这对伽马射线暴和活动星系核的模型有着重要的意义，这些模型在该框架中以低得多的能量发出光束。
Relativistic reconnection has been invoked as a mechanism for particle acceleration in numerous astrophysical systems. According to idealized analytical models, reconnection produces a bulk relativistic outflow emerging from the reconnection sites (X-points). The resulting radiation is therefore highly beamed. Using two-dimensional particle-in-cell simulations, we investigate particle and radiation beaming, finding a very different picture. Instead of having a relativistic average bulk motion with an isotropic electron velocity distribution in its rest frame, we find that the bulk motion of the particles in X-points is similar to their Lorentz factor γ, and the particles are beamed within . On the way from the X-point to the magnetic islands, particles turn in the magnetic field, forming a fan confined to the current sheet. Once they reach the islands they isotropize after completing a full Larmor gyration and their radiation is no longer strongly beamed. The radiation pattern at a given frequency depends on where the corresponding emitting electrons radiate their energy. Lower-energy particles that cool slowly spend most of their time in the islands and their radiation is not highly beamed. Only particles that quickly cool at the edge of the X-points generate a highly beamed fan-like radiation pattern. The radiation emerging from these fast cooling particles is above the burn-off limit (∼100 MeV in the overall rest frame of the reconnecting plasma). This has significant implications for models of gamma-ray bursts and active galactic nuclei that invoke beaming in that frame at much lower energies.