Nonradiative shocks accelerate particles and heat astrophysical plasmas. While supernova remnants are the most well-studied example, neutron star (NS) bow shocks are also nonradiative and Balmer dominated. NS bow shocks are likely ubiquitous in the interstellar medium due to their large speeds imparted at birth, and they are thought to be a discrete source population contributing to the Galactic cosmic-ray spectrum. To date, nine NS bow shocks have been directly observed in Hα images. Most of these shocks have been characterized using narrowband Hα imaging and slit spectroscopy, which do not resolve the multicomponent velocity structure of the shocks and their spatial geometry. Here we present integral field spectroscopy of three NS bow shocks: J0742−2822, J1741−2054, and J2225+6535 (the Guitar Nebula). We measure the shock properties simultaneously in four dimensions: the 2D projected shock morphology, the radial velocity structure, and the Hα flux. The broad-to-narrow line ratio (I _b/I _n) is inferred from radial velocity profiles, and for J1741−2054, the narrow line is detected in multiple regions of the shock. The inferred line ratios and widths suggest that NS bow shocks represent a low-shock velocity regime (V ≲ 200 km s⁻¹) in which I _b/I _n is high, distinct from the shock regime probed by supernova remnants. Our results illustrate a need for nonradiative shock models at velocities lower than previously considered, which will reveal the electron–ion temperature ratios and particle acceleration efficiencies of these bow shocks.

中文翻译：

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用中子星弓激波探测非辐射激波的低速状态


非辐射冲击会加速粒子并加热天体物理等离子体。虽然超新星残骸是研究最充分的例子，但中子星 （NS） 弓激波也是非辐射性的，并且以 Balmer 为主。NS 弓激波在星际介质中可能无处不在，因为它们在出生时具有很大的速度，并且它们被认为是对银河宇宙射线光谱做出贡献的离散源群。迄今为止，已在 Hα 图像中直接观察到 9 次 NS 弓激波。这些激波中的大多数已经使用窄带 Hα 成像和狭缝光谱进行了表征，它们无法解析激波的多分量速度结构及其空间几何形状。在这里，我们展示了三种 NS 弓激波的积分场谱：J0742−2822、J1741−2054 和 J2225+6535（吉他星云）。我们同时在四个维度上测量冲击特性：二维投影冲击形态、径向速度结构和 Hα 磁通量。宽线与窄线比 （I_b/I_n） 是从径向速度分布推断出来的，对于 J1741-2054，在激波的多个区域检测到窄线。推断的线比和宽度表明，NS 弓激波代表低冲击速度状态 （V ≲ 200 km s⁻¹），其中 I_b/I_n 很高，与超新星残余物探测的激波状态不同。我们的结果表明，需要以低于以前考虑的速度进行非辐射冲击模型，这将揭示这些弓形激波的电子-离子温度比和粒子加速效率。