Scintillation spectra of some pulsars have suggested the existence of ≲ AU scale density structures in the ionized interstellar medium, whose astrophysical correspondence is still a mystery. The detailed study of Brisken et al. suggested two possible morphologies for these structures: A parallel set of filaments or sheets (the ‘parallel stripes model’), or a filament broken up into denser knots (the ‘threaded beads model’). Here, we propose a straightforward test that can distinguish these two morphologies: Whether the apex of the main parabolic arc created by the scattered images deviates from the origin of the scintillation spectrum or not. In the ‘parallel stripes’ model, the scattered images move along the stripes as the relative position of the pulsar moves. As a result, the pulsar is always co-linear with the scattered images, and thus, the apex of the main parabolic arc stays at the origin of the scintillation spectrum. In the ‘threaded beads’ model, the scattered images remain at almost fixed positions relative to the density structures, and thus, the pulsar is not co-linear with the scattered images at most times, leading to an offset between the apex and the origin. Looking for this possible offset in a large sample of pulsar scintillation spectra, or monitoring the evolution of parabolic arcs will help pin down the morphology of these tiny density structures and constrain their astrophysical origin.

中文翻译：

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星际介质中太阳系尺度等离子体透镜的形态学：脉冲星闪烁抛物弧的测试

一些脉冲星的闪烁光谱表明在电离的星际介质中存在≲ AU 尺度密度结构，其天体物理对应仍然是一个谜。Brisken 等人的详细研究。为这些结构提出了两种可能的形态：一组平行的细丝或薄片（“平行条纹模型”），或者将细丝分解成更密集的结（“螺纹珠模型”）。在这里，我们提出了一个可以区分这两种形态的简单测试：由散射图像产生的主抛物线弧的顶点是否偏离闪烁光谱的原点。在“平行条纹”模型中，随着脉冲星的相对位置移动，散射图像沿着条纹移动。结果，脉冲星总是与散射图像共线，因此，主抛物线弧的顶点停留在闪烁光谱的原点。在“螺纹珠”模型中，散射图像相对于密度结构保持在几乎固定的位置，因此脉冲星在大多数时候与散射图像不共线，导致顶点与原点之间存在偏移. 在大量脉冲星闪烁光谱样本中寻找这种可能的偏移量，或监测抛物线弧的演变，将有助于确定这些微小密度结构的形态并限制它们的天体物理起源。导致顶点和原点之间的偏移。在大量脉冲星闪烁光谱样本中寻找这种可能的偏移量，或监测抛物线弧的演变，将有助于确定这些微小密度结构的形态并限制它们的天体物理起源。导致顶点和原点之间的偏移。在大量脉冲星闪烁光谱样本中寻找这种可能的偏移量，或监测抛物线弧的演变，将有助于确定这些微小密度结构的形态并限制它们的天体物理起源。