标题： 使用 LOFAR 观测类型 II 射电爆发解析空间和时间冲击结构 显示英文标题

标题： Resolving spatial and temporal shock structures using LOFAR observations of type II radio bursts

摘要： 无碰撞激波是宇宙中最强大的粒子加速器之一。 在日球层中，II型太阳射电爆发是被太阳发出的无碰撞激波加速的电子的标志。 这些爆发的光谱观测显示了多种精细结构，这些结构通常由多个II型频带组成。 这些频带和结构的起源尚不明确，被认为与传播激波周围的不均匀环境有关。 在此，我们旨在利用2023年10月3日观测到的一个复杂II型射电爆发的高分辨率射电成像观测，确定日冕激波附近的大型局部结构。 通过使用低频阵列（LOFAR）的干涉成像，结合极紫外观测，我们研究了相对于传播激波的低频（30--80~MHz）多个II型频带的起源。 我们在米波波长识别出至少三个射电源，对应于多频带II型爆发。 II型爆发源随着由日冕物质抛射驱动的激波向外传播。 我们发现了一个双射电源，其分离度随时间增加，与全球日冕激波的膨胀速率一致。 这表明整体激波膨胀几乎是自相似的，加速热点在不同时间形成，并以与激波膨胀速率成比例的速率分裂。 我们的结果表明，提高空间分辨率对于确定日冕激波的小尺度空间特性或周围介质的结构至关重要。 可能的激波波动或上游等离子体在10$^5$~km尺度上的结构可以作为超热电子加速的热点。 显示英文摘要

摘要： Collisionless shocks are one of the most powerful particle accelerators in the Universe. In the heliosphere, type II solar radio bursts are signatures of electrons accelerated by collisionless shocks launched at the Sun. Spectral observations of these bursts show a variety of fine structures often composing multiple type II lanes. The origin of these lanes and structures is not well understood and has been attributed to the inhomogeneous environment around the propagating shock. Here, we aim to determine the large-scale local structures near a coronal shock wave using high-resolution radio imaging observations of a complex type II radio burst observed on 3 October 2023. By using inteferometric imaging from the Low Frequency Array (LOFAR), combined with extreme ultraviolet observations, we investigate the origin of multiple type II lanes at low frequencies (30--80~MHz) relative to the propagating shock wave. We identify at least three radio sources at metric wavelengths corresponding to a multi-lane type II burst. The type II burst sources propagate outwards with a shock driven by a coronal mass ejection. We find a double radio source that exhibits increasing separation over time, consistent with the expansion rate of the global coronal shock. This suggests that the overall shock expansion is nearly self-similar, with acceleration hotspots forming at various times and splitting at a rate proportional to the shock's expansion. Our results show the importance of increased spatial resolution in determining either the small-scale spatial properties in coronal shocks or the structuring of the ambient medium. Possible shock corrugations or structuring of the upstream plasma at the scale of 10$^5$~km can act as hotspots for the acceleration of suprathermal electrons.