Probing the low-velocity regime of non-radiative shocks with neutron star bow shocks
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| Format: | Preprint |
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2024
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| _version_ | 1866910653794484224 |
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| author | Ocker, S. K. Cosens, M. |
| author_facet | Ocker, S. K. Cosens, M. |
| contents | Non-radiative shocks accelerate particles and heat astrophysical plasmas. While supernova remnants are the most well-studied example, neutron star (NS) bow shocks are also non-radiative 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 H$α$ images. Most of these shocks have been characterized using narrowband H$α$ imaging and slit spectroscopy, which do not resolve the multi-component velocity structure of the shocks and their spatial geometry. Here we present integral field spectroscopy of three NS bow shocks: J0742$-$2822, J1741$-$2054, and J2225$+$6535 (the Guitar Nebula). We measure the shock properties simultaneously in four dimensions: the 2D projected shock morphology, the radial velocity structure, and the H$α$ flux. The broad-to-narrow line ratio ($I_{\rm b}/I_{\rm n}$) 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 \lesssim 200$ km/s) in which $I_{\rm b}/I_{\rm n}$ is high, distinct from the shock regime probed by supernova remnants. Our results illustrate a need for non-radiative shock models at velocities lower than previously considered, which will reveal the electron-ion temperature ratios and particle acceleration efficiencies of these bow shocks. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2409_13525 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Probing the low-velocity regime of non-radiative shocks with neutron star bow shocks Ocker, S. K. Cosens, M. High Energy Astrophysical Phenomena Non-radiative shocks accelerate particles and heat astrophysical plasmas. While supernova remnants are the most well-studied example, neutron star (NS) bow shocks are also non-radiative 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 H$α$ images. Most of these shocks have been characterized using narrowband H$α$ imaging and slit spectroscopy, which do not resolve the multi-component velocity structure of the shocks and their spatial geometry. Here we present integral field spectroscopy of three NS bow shocks: J0742$-$2822, J1741$-$2054, and J2225$+$6535 (the Guitar Nebula). We measure the shock properties simultaneously in four dimensions: the 2D projected shock morphology, the radial velocity structure, and the H$α$ flux. The broad-to-narrow line ratio ($I_{\rm b}/I_{\rm n}$) 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 \lesssim 200$ km/s) in which $I_{\rm b}/I_{\rm n}$ is high, distinct from the shock regime probed by supernova remnants. Our results illustrate a need for non-radiative shock models at velocities lower than previously considered, which will reveal the electron-ion temperature ratios and particle acceleration efficiencies of these bow shocks. |
| title | Probing the low-velocity regime of non-radiative shocks with neutron star bow shocks |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2409.13525 |