Fast radio bursts (FRBs) can be scattered by ionized gas in their local environments, host galaxies, intervening galaxies along their lines-of-sight, 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 line-of-sight. 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 $τ\propto(\tilde{F} \times {\rm DM}^2) A_τ$, where ${\rm DM}$ is the dispersion measure, $\tilde{F}$ quantifies electron density variations with $\tilde{F}=0$ 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 $\tilde{F}$ is at least an order of magnitude smaller in the halo than in the Galactic disk. The maximum pulse broadening from the halo is $τ\lesssim12$ $μ$s at 1 GHz. We compare our analysis of the Milky Way halo with other galaxy haloes by placing limits on the scattering contributions from haloes intersecting the lines-of-sight to FRB 181112 and FRB 191108. Our results are consistent with haloes making negligible or very small contributions to the scattering times of these FRBs.
Constraining the Binarity of Massive Black Holes in the Galactic Center and Some Nearby Galaxies via Pulsar Timing Array Observations of Gravitational Waves
Constraining the origin of the nanohertz gravitational-wave background by pulsar timing array observations of both the background and individual supermassive binary black holes
Constraining the shape of dark matter haloes using only starlight II. Tests of the technique with objects of known gravitational potential
Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Universidad de La Laguna（拉古纳大学）；Universidad Nacional del Noroeste de la Prov. de Buenos Aires, UNNOBA, CONICET（布宜诺斯艾利斯省西北国立大学，UNNOBA，CONICET）；University of Virginia（弗吉尼亚大学）
FLAMINGO: Tracing the co-evolution of hot gas and black holes in galaxy groups and clusters
Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）；Institute for Computational Cosmology, Department of Physics, University of Durham（杜伦大学物理学院计算宇宙学研究所）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Lorentz Institute for Theoretical Physics, Leiden University（莱顿大学洛伦兹理论物理研究所）
