Fast radio bursts (FRBs) can be scattered by ionized gas in their local environments, host galaxies, intervening galaxies along their lines of sight (LOS), the intergalactic medium, and the Milky Way. The relative contributions of these different media depend on their geometric configuration and the internal properties of the gas. When these relative contributions are well understood, FRB scattering is a powerful probe of density fluctuations along the LOS. The precise scattering measurements for FRB 121102 and FRB 180916 allow us to place an upper limit on the amount of scattering contributed by the Milky Way halo to these FRBs. The scattering time , where DM is the dispersion measure, quantifies electron density variations with for a smooth medium, and the dimensionless constant A _τ quantifies the difference between the mean scattering delay and the 1/e scattering time typically measured. A likelihood analysis of the observed scattering and halo DM constraints finds that is at least an order of magnitude smaller in the halo than in the Galactic disk. The maximum pulse broadening from the halo is τ ≲ 12 μs at 1 GHz. We compare our analysis of the Milky Way halo with other galaxy halos by placing limits on the scattering contributions from halos intersecting the LOS to FRB 181112 and FRB 191108. Our results are consistent with halos making negligible or very small contributions to the scattering times of these FRBs.

快速射电暴 (FRB) 可以被局部环境中的电离气体、宿主星系、沿视线 (LOS) 的干预星系、星系际介质和银河系散射。这些不同介质的相对贡献取决于它们的几何构型和气体的内部特性。当这些相对贡献被很好地理解时，FRB 散射是一个强大的探测沿 LOS 的密度波动。FRB 121102 和 FRB 180916 的精确散射测量使我们能够对银河系晕对这些 FRB 贡献的散射量设置上限。散射时间，其中 DM 是色散度量，量化了光滑介质的电子密度变化，以及无量纲常数A _τ 量化平均散射延迟和通常测量的 1/ e散射时间之间的差异。对观测到的散射和光晕 DM 约束的似然分析发现光晕中的光晕至少比银河盘中的小一个数量级。来自晕圈的最大脉冲展宽为τ ≲ 12 μ s，频率为 1 GHz。我们通过限制与 LOS 相交的晕对 FRB 181112 和 FRB 191108 的散射贡献来比较我们对银河系晕与其他星系晕的分析。我们的结果与晕对这些散射时间的贡献可以忽略不计或非常小一致FRB。