离散度测量：混淆度、常数和清晰度
Dispersion measure: Confusion, Constants & Clarity
摘要：
频散测度是射电暴和快速射电暴的重要特征之一。有一个错误的观点，认为DM是一个精确的测量之间的观察者和源的电子柱密度。首先，DM与真正的柱密度不同，它不是洛伦兹不变量。其次，DM还包括来自离子的贡献，并且对中间云中的等离子体的温度敏感。单独地，主要可观测值是色散斜率$\mathcal{D}\equiv Δ{(t)}/Δ{(ν^{-2}})$，其中$t(ν)$是频率处的到达时间$ν$。将$\mathcal{D}$转换为DM需要一个由物理常数和天文常数组成的比例因子。在脉冲星天文学的早期，相关的常数被定义为百万分之一（ppm）。因此，产生了一种固定换算系数的惯例。随着时间的推移，出现了几个这样的惯例--这是造成混乱的原因。与此同时，在过去的几年里，国际单位制已经被重组，秒差距现在被准确地定义。结果，转换因子的当前精度低于十亿分之一--比$\mathcal{D}$的最佳测量误差好许多数量级。我们现在处于一个尴尬的境地，其中主要的“可观察”，DM，具有不正确的缩放因子。为了解决这两个问题，我建议天文学家报告主要测量值$\mathcal{D}$（建议标准化为$10^{15}\,$ Hz），而不是DM。感兴趣的用户可以将$\mathcal{D}$转换为DM，而不需要知道脉冲星计时社区的秘密握手。
英文摘要：
The dispersion measure (DM) is one of the key attributes of radio pulsars and Fast Radio Bursts (FRBs). There is a mistaken view that the DM is an accurate measure of the column density of electrons between the observer and the source. To start with, the DM, unlike a true column density, is not a Lorentz invariant. Next, the DM also includes contribution from ions and is sensitive to the temperature of the plasma in the intervening clouds. Separately, the primary observable is the dispersion slope, $\mathcal{D}\equiv Δ{(t)}/Δ{(ν^{-2}})$, where $t(ν)$ is the arrival time at frequency, $ν$. A scaling factor composed of physical and astronomical constants is needed to convert $\mathcal{D}$ to DM. In the early days of pulsar astronomy the relevant constants were defined to parts per million (ppm). As a result, a convention arose in which this conversion factor was fixed. Over time, several such conventions came about -- recipe for confusion. Meanwhile, over the past several years, the SI system has been restructured and the parsec is now exactly defined. As a result, the present accuracy of the conversion factor is below a part per billion -- many orders of magnitude better than the best measurement errors of $\mathcal{D}$. We are now in an awkward situation wherein the primary "observable", the DM, has incorrect scaling factor(s). To address these two concerns I propose that astronomers report the primary measurement, $\mathcal{D}$ (with a suggested normalization of $10^{15}\,$Hz), and not the DM. Interested users can convert $\mathcal{D}$ to DM without the need to know secret handshakes of the pulsar timing communities.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
