The Scattering and Intrinsic Structure of Sagittarius A* at Radio Wavelengths
The Scattering and Intrinsic Structure of Sagittarius A* at Radio Wavelengths
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DOI：
10.3847/1538-4357/aadcff
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发表时间：
2018-08
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通讯作者：
Michael D. Johnson;R. Narayan;D. Psaltis;L. Blackburn;Y. Kovalev;C. Gwinn;Guangyao Zhao;G. Bower-G.-Bow
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作者：
Michael D. Johnson;R. Narayan;D. Psaltis;L. Blackburn;Y. Kovalev;C. Gwinn;Guangyao Zhao;G. Bower-G.-Bow
银河系中心超大质量黑洞人马座A*（Sgr A*）的射电图像主要是星际散射。以前对Sgr A* 的研究采用了各向异性高斯模型来描述本征源和散射，并且他们使用纯λ2标度来外推散射以估计本征性质。然而，物理激励源和散射模型打破了所有这三个假设。他们还预测折射散射效应将是显著的，这在标准模型拟合程序中被忽略了。我们分析无线电观测的Sgr A* 使用物理激励的散射模型，我们开发了一个处方，将折射散射的不确定性模型拟合时。我们表明，各向异性高斯散射内核是一个很好的近似Sgr A* 在波长大于1厘米，与一个角度大小的沿着长轴，沿着短轴，和一个位置角。我们估计湍流耗散尺度至少为600 km，暂时支持rin = 800 ± 200 km，这表明离子拉莫尔半径定义了耗散尺度。我们发现散射物质中密度涨落的幂律指数β < 3.47，比柯尔莫哥洛夫谱（β = 11/3）的预期要浅，我们在rin = 800 km的情况下进行了估计。我们发现Sgr A* 的固有结构在1.3 mm至1.3 cm的波长范围内几乎是各向同性的，其尺寸大致与波长成比例：我们讨论的影响模型的Sgr A*，星际湍流的理论，并与事件视界望远镜成像Sgr A*。
Radio images of the Galactic Center supermassive black hole, Sagittarius A* (Sgr A*), are dominated by interstellar scattering. Previous studies of Sgr A* have adopted an anisotropic Gaussian model for both the intrinsic source and the scattering, and they have extrapolated the scattering using a purely λ2 scaling to estimate intrinsic properties. However, physically motivated source and scattering models break all three of these assumptions. They also predict that refractive scattering effects will be significant, which have been ignored in standard model fitting procedures. We analyze radio observations of Sgr A* using a physically motivated scattering model, and we develop a prescription to incorporate refractive scattering uncertainties when model fitting. We show that an anisotropic Gaussian scattering kernel is an excellent approximation for Sgr A* at wavelengths longer than 1 cm, with an angular size of along the major axis, along the minor axis, and a position angle of . We estimate that the turbulent dissipation scale is at least 600 km, with tentative support for rin = 800 ± 200 km, suggesting that the ion Larmor radius defines the dissipation scale. We find that the power-law index for density fluctuations in the scattering material is β < 3.47, shallower than expected for a Kolmogorov spectrum (β = 11/3), and we estimate in the case of rin = 800 km. We find that the intrinsic structure of Sgr A* is nearly isotropic over wavelengths from 1.3 mm to 1.3 cm, with a size that is roughly proportional to wavelength: . We discuss implications for models of Sgr A*, for theories of interstellar turbulence, and for imaging Sgr A* with the Event Horizon Telescope.