Electron energization at quasi-perpendicular oblique shocks in Supernova remnants

超新星遗迹中准垂直斜激波的电子赋能

• 批准号: 451321940
• 负责人: Professor Dr. Martin Karl Wilhelm Pohl
• 金额: --
• 依托单位: Institut für Physik und Astronomie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/451321940?language=en
• 关键词: Electron; energization; quasi; perpendicular; oblique

Most of the available information about particle acceleration in astrophysical objects relates to electrons, on account of their high radiation efficiency. Not as much is known, however, as to how electrons get accelerated. Electron participation in diffusive shock acceleration at Supernova-remnant shocks requires that they be pre-accelerated to Lorentz factors above 100. Where and how that happens is the focus of this project. Supernova shocks have nonrelativistic propagation velocities and are characterized by high sonic and Alfv ́enic Mach numbers. The physics of non-relativistic shocks is governed by reflection of particles, the interaction of which with the incoming plasma excites a variety of instabilities upstream of the shock. If the magnetic field is oriented quasi-parallel to the shock normal, ions can travel far and drive instabilities in the far-upstream region. For quasi-perpendicular shocks the reflected ions are not fast enough and essentially conduct only one Larmor orbit, but electrons may stream along the magnetic field toward the far upstream region and drive waves there. We use fully kinetic Particle-In-Cell simulations to study these processes, and electron acceleration in particular, at oblique quasi-perpendicular shocks, building on methods and results obtained for strictly perpendicular shocks. At shocks a fraction of the upstream ion kinetic energy goes to electrons though different channels: shock surfing acceleration, shock drift acceleration, acceleration by shock potential, magnetic reconnection, stochastic interaction with magnetic turbulences, etc. Changing the angle between the large-scale magnetic field and the shock normal, we expect to determine the changes in the contribution of individual acceleration mechanisms to particle energization and hence be able to establish the rate of electron injection into diffusive shock acceleration as function of the shock obliquity. The essential output of the project will be the upstream and downstream electron spectra, the efficiency of electron reflection off the shock, and the type and behaviour of plasma instabilities they drive. We shall also explore the scaling of the results with the ion-to-electron mass ratio used in the simulation. Our results will inform global models of electron acceleration at SNR shocks.It is known that the late-time evolution of shocks involves large-scale disturbance of the shock front and the pre-shock medium that are seeded by faster processes like currents carried by reflected particles in the upstream medium whose existence and properties are well captured with the full PIC method, and that is what we are going to do. We posit that the long-wavelength disturbance is almost inevitable once the current startsbecause there will always be small variations in that current. Our project will establish with what efficiency the currents are generated.

由于电子的高辐射效率，大多数有关天体物理物体中粒子加速的可用信息都与电子有关。 然而，对于电子如何加速，人们知之甚少。电子参与超新星遗迹激波的扩散激波加速需要将它们预加速到洛伦兹因子高于 100。这种情况发生的地点和方式是该项目的重点。超新星激波具有非相对论性传播速度，并具有高音速和阿尔夫马赫数的特征。非相对论性激波的物理过程受粒子反射的控制，粒子与进入的等离子体的相互作用激发了激波上游的各种不稳定性。如果磁场的方向与激波法线准平行，则离子可以传播很远并导致上游区域的不稳定。对于准垂直激波，反射离子的速度不够快，并且基本上仅传导一个拉莫尔轨道，但电子可以沿着磁场流向较远的上游区域并在那里驱动波。我们基于严格垂直激波所获得的方法和结果，使用全动力学细胞内粒子模拟来研究这些过程，特别是在倾斜准垂直激波下的电子加速。在冲击时，上游离子动能的一小部分通过不同的通道传递给电子：冲击冲浪加速、冲击漂移加速、冲击势加速、磁重联、与磁湍流的随机相互作用等。改变大尺度磁场和冲击法向之间的角度，我们期望确定单个加速机制对粒子能量贡献的变化，从而能够确定电子注入到粒子的速率。 扩散激波加速度作为激波倾角的函数。该项目的基本输出将是上游和下游电子光谱、激波的电子反射效率以及它们驱动的等离子体不稳定性的类型和行为。我们还将探索结果与模拟中使用的离子与电子质量比的比例。我们的结果将为SNR激波下电子加速的全局模型提供信息。众所周知，激波的后期演化涉及激波前沿和激波前介质的大规模扰动，这些扰动是由更快的过程产生的，例如上游介质中反射粒子携带的电流，其存在和特性可以通过完整的PIC方法很好地捕获，这就是我们要做的。我们假设，一旦电流开始，长波长干扰几乎是不可避免的，因为电流总是存在微小的变化。我们的项目将确定电流产生的效率。