发表机构
The Johns Hopkins University Applied Physics Laboratory; University of Turku; University of California, San Diego; Eureka Scientific; Ben Gurion University of the Negev; KU Leuven; California Institute of Technology; University of California, Berkeley; Princeton University（约翰斯·霍普金斯大学应用物理实验室; 图尔库大学; 加州大学圣迭戈分校; 尤里卡科学公司; 本-古里安大学; 鲁汶大学; 加州理工学院; 加州大学伯克利分校; 普林斯顿大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
帕克太阳探测器在0.24天文单位处观测到近平行激波，发现粒子约束边界随剩余时间呈幂律下降，表明激波前兆的粒子约束刚性由流动粒子自生波的增长速率决定。
AI 中文摘要
无碰撞激波通过其自身驱动的上游波场约束其所加速的粒子。流动粒子共振放大阿尔芬波，而这些波随后通过俯仰角散射约束相同的粒子。因此，激波前兆能保持的刚性受限于这些波增长的速度，而这种耦合此前从未在任何行星际激波处进行过原位约束。在此，我们报告帕克太阳探测器于2023年3月13日在0.24天文单位处对一次快速、近平行的日冕物质抛射驱动的激波的测量结果，该测量通过其加速的高能粒子群体约束了这种波粒耦合。我们测量了谱折叠能量，即被约束质子与向上游逃逸质子之间的边界，发现它从约6 MeV降至约1.5 MeV，满足$E_\mathrm{fold}\propto\Delta t^{\\,\alpha}$，其中$\alpha\simeq0.34$，$\Delta t$为激波到达前剩余的时间。在到达前一个前兆对流时间内，该边界位于$E_\mathrm{c}\simeq 2.46$ MeV，这是尺度为$L_\mathrm{EP}$的前兆的特征约束能量。通过准线性边际稳定性条件解读，同样的演化意味着共振波增长时标$\tau_\mathrm{growth}(E)\propto E^{1/\alpha}\simeq E^{2.92}$，该时标在$E_\mathrm{c}$以上超过前兆对流时间。激波后的俯仰角各向异性在2–5 MeV处跨越相同的约束-逃逸转变时符号反转。因此，激波前兆能约束粒子的刚性，在原位由流动粒子群体构建自身约束波的速度所决定。
英文摘要
Collisionless shocks confine the particles they accelerate with the upstream wave field they themselves drive. Streaming particles resonantly amplify Alfvén waves, and the waves then confine the same particles by pitch-angle scattering. The rigidity a shock precursor can hold is therefore capped by how fast those waves grow, and that coupling has not previously been constrained in-situ at any interplanetary shock. Here we report Parker Solar Probe measurements of a fast, near-parallel coronal mass ejection-driven shock at 0.24~AU on 2023 March 13 that constrain this wave-particle coupling through the energetic-particle population it accelerates. We measure the spectral folding energy, the boundary between the confined and the upstream-escaping protons, and find that it falls from $\sim$6 to $\sim$1.5~MeV as $E_\mathrm{fold}\proptoΔt^{\,α}$ with $α\simeq0.34$, where $Δt$ is the time remaining before shock arrival. One precursor convective time before arrival this boundary is at $E_\mathrm{c}\simeq 2.46$~MeV, a characteristic confinement energy of a precursor of scale $L_\mathrm{EP}$. Read through the quasi-linear marginal-stability condition, the same evolution implies a resonant wave-growth timescale $τ_\mathrm{growth}(E)\propto E^{1/α}\simeq E^{2.92}$ that exceeds the precursor convective time above $E_\mathrm{c}$. The post-shock pitch-angle anisotropy reverses sign across the same confinement--escape transition at 2--5~MeV. The rigidity to which a shock precursor can confine particles is therefore set, in-situ, by how quickly the streaming population builds its own confining waves.
Comments15 pages, 6 figures, Accepted in The Astrophysical Journal Letters
