论文标题
分散度量：混乱，常数和清晰度
Dispersion measure: Confusion, Constants & Clarity
论文作者
论文摘要
色散度量（DM）是无线电脉冲星和快速无线电爆发（FRB）的关键属性之一。错误的观点是，DM是观察者和源之间电子柱密度的准确度量。首先，与真实的柱密度不同，DM并不是Lorentz不变的。接下来，DM还包括离子的贡献，并且对中间云中的血浆温度敏感。另外，可观察到的主要是分散斜率，$ \ Mathcal {d} \equivΔ{（t）}/δ{（ν^{ - 2}}）$，其中$ t（ν（ν）$是频率到达的时间，$ν$。需要由物理和天文常数组成的缩放因子将$ \ Mathcal {d} $转换为DM。在Pulsar天文学的早期，相关常数定义为百万（PPM）。结果，出现了固定该转换因子的惯例。随着时间的流逝，发生了一些这样的惯例 - 混乱的食谱。同时，在过去的几年中，SI系统已进行了重组，并且PARSEC现在已完全定义。结果，转换因子的当前准确性低于十亿美元的一部分 - 许多数量级要比$ \ Mathcal {d} $的最佳测量错误要好。现在，我们处于尴尬境地，其中主要“可观察到的” DM具有不正确的缩放系数。为了解决这两个问题，我建议天文学家报告主要测量值，$ \ MATHCAL {D} $（建议的标准化为$ 10^{15} \，$ Hz），而不是DM。有兴趣的用户可以将$ \ Mathcal {D} $转换为DM，而无需了解Pulsar定时社区的秘密握手。
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.
