Density power spectrum in the local interstellar medium
Density power spectrum in the local interstellar medium
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DOI：
10.1038/291561a0
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发表时间：
1981-06
期刊：
影响因子：
64.8
通讯作者：
J. Armstrong;J. Cordes;B. Rickett
中科院分区：
文献类型：
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作者：
J. Armstrong;J. Cordes;B. Rickett
自从星际闪烁被发现以来，星际介质（ISM）就被认为含有尺度为109 m的电子密度涨落。这些不规则性的散射特性已被用于脉冲星和连续源的研究，并调查小尺度湍流本身1 -11。(We这里用“湍流”来表示无序、不规则的流动。）如果ISM湍流在足够宽的波动尺度范围内延伸，它可能在银河宇宙线传输和约束中发挥重要作用12 -14。在这里，我们提出的观测证据表明，电子密度的不规则性存在于一个非常广泛的规模大小。波数范围为<$10 −11-10− 6 m − 1的射电散射观测结果与波数为−3.7±0.6的密度谱相一致。在较低的空间波数（10−16-10− 18 m −1）下，功率谱可以通过计算光谱“外”尺度附近的密度波动15，与ISM理论模型预测的密度不规则性16进行比较，并与速度结构函数的观测结果13，17，18进行比较来估计。当与高波数（射电）数据结合时，这些低波数谱估计最简单地解释为在12十进位尺度范围内（100 pc到107 m）表现为（波数）-3.6 ± 0.2的密度谱。然而，这样的光谱可能存在理论上的困难12，14，19。或者，低波数数据可以与ISM云相关联，ISM云在物理上与小尺度湍流不同。
Since the identification of interstellar scintillation, the interstellar medium (ISM) has been known to contain electron density fluctuations having scales ∼109m. The scattering properties of these irregularities have been used in pulsar and continuum source studies and to investigate the small scale turbulence itself1–11. (We use ‘turbulence’ here to imply a disordered, irregular flow.) If the ISM turbulence extends over a broad enough range of fluctuation scales, it could have an important role in galactic cosmic ray transport and confinement12–14. Here we present observational evidence that electron density irregularities exist over a very wide range of scale sizes. Radio scattering observations associated with the wavenumber range ∼10−11–10−6m−1are consistent with a density spectrum of the form (wavenumber)−3.7±0.6. At lower spatial wavenumbers (10−16–10−18m−1) the power spectrum can be estimated by computation of the density fluctuations near the ‘outer’ scale of the spectrum15, comparison with density irregularities predicted by theoretical models of the ISM16, and comparison with observations of the velocity structure function13,17,18. When combined with the high-wavenumber (radio) data, these low-wavenumber spectrum estimates are most simply interpreted in terms of a density spectrum behaving as (wavenumber)−3.6±0.2over a 12 decade scale size range (∼100 pc to ∼107m). There may be theoretical difficulties12,14,19with such a spectrum, however. Alternatively, the low-wavenumber data could be associated with ISM clouds which are physically distinct from the small scale turbulence.