Acceleration of suprathermal protons near an interplanetary shock
Acceleration of suprathermal protons near an interplanetary shock
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行星际激波附近超热质子的加速
DOI：
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发表时间：
2023
期刊：
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通讯作者：
G. Ho
中科院分区：
文献类型：
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作者：
L. Yang;V. Heidrich;L. Berger;R. Wimmer–Schweingruber;L. Wang;J. He;X. Zhu;D. Duan;A. Kollhoff;D. Pacheco;P. Kühl;Z. Xu;D. Keilbach;J. Rodríguez;G. Ho
上下文。众所周知，行星际无碰撞激波是高能带电粒子的来源，最高可达数百MeV。然而，潜在的加速机制仍在争论中。目标。我们利用太阳轨道飞行器上高能粒子探测器的超热电子质子传感器史无前例的高分辨率测量，确定了2021年11月3日行星际激波加速的超热质子的性质，以约束潜在的激波加速机制。方法：研究方法。我们首次fi重建了太阳风架中超热质子的俯仰角分布(PAD)。然后，我们研究了PADS、时间flUX PROfiLE的演化，以及激波附近质子布居的速度分布函数，并将观测结果与理论预测进行了比较。结果。我们fi发现，超热质子fl在上游区的激波前出现峰值∼12到∼24s。质子flux在下游激波附近的薄层(∼8000 km)内迅速减少∼50%，并在更远的下游变得恒定。此外，在fi1000−3600 kms−1时，上游(下游)区域的质子速度分布函数为f(V)∼v−−，γ为∼3。4±0。2(∼4.3±0。7)在∼1800±100 kms−1(∼1600±200 kms−1)和γOf∼5的断裂下的速度(V)。8±0。3(∼5.8±0。2)速度高于此速度。这些指数都小于fi一阶费米加速的预测值。此外，在覆盖的俯仰角范围内，质子垫在靠近上游区域的远离激波的方向上表现出各向异性，并在更靠上游的区域变得接近各向同性，而在激波下游，它们表现出向90◦PA的各向异性的趋势。结论。这些结果表明，在行星际激波中，超热质子的加速在∼10s的时间尺度上是动态的，即很少的质子回转周期。此外，激波漂移加速很可能在加速这些超热质子方面发挥重要作用。
Context. Interplanetary collisionless shocks are known to be sources of energetic charged particles up to hundreds of MeV. However, the underlying acceleration mechanisms are still under debate. Aims. We determine the properties of suprathermal protons accelerated by the interplanetary shock on 2021 November 3 with the unprecedented high-resolution measurements by the SupraThermal Electron Proton sensor of the Energetic Particle Detector on board the Solar Orbiter spacecraft, in order to constrain the potential shock acceleration mechanisms. Methods. We first reconstructed the pitch-angle distributions (PADs) of suprathermal protons in the solar wind frame. Then, we studied the evolution of the PADs, the temporal flux profile, and the velocity distribution function of this proton population close to the shock and compared the observations to theoretical predictions. Results. We find that the suprathermal proton fluxes peak ∼ 12 to ∼ 24s before the shock in the upstream region. The proton fluxes rapidly decrease by ∼ 50% in a thin layer ( ∼ 8000km) adjacent to the shock in the downstream region and become constant farther downstream. Furthermore, the proton velocity distribution functions in the upstream (downstream) region fit a double power law, f ( v ) ∼ v − γ , at ∼ 1000 − 3600kms − 1 , with a γ of ∼ 3 . 4 ± 0 . 2 ( ∼ 4 . 3 ± 0 . 7) at velocities ( v ) below a break at ∼ 1800 ± 100kms − 1 ( ∼ 1600 ± 200kms − 1 ) and a γ of ∼ 5 . 8 ± 0 . 3 ( ∼ 5 . 8 ± 0 . 2) at velocities higher than this. These indices are all smaller than predicted by first-order Fermi acceleration. In addition, the proton PADs in the covered pitch-angle range show anisotropies in the direction away from the shock in the region close to the upstream region and become nearly isotropic farther upstream, while downstream of the shock, they show a tendency of anisotropies towards 90 ◦ PA. Conclusions. These results suggest that the acceleration of suprathermal protons at interplanetary shocks are dynamic on a timescale of ∼ 10s, that is, few proton gyroperiods. Furthermore, shock-drift acceleration likely plays an important role in accelerating these suprathermal protons.