National Research Council of Canada. National Science Infrastructure
Intergalactic medium; Large-scale structure of universe; Radiation mechanisms; Radio continuum; Solar wind; Sun; Coronal mass ejections (CMEs)
We empirically evaluate the scheme proposed by Lieu & Duan in which the light curve of a time-steady radio source is predicted to exhibit increased variability on a characteristic timescale set by the sightline's electron column density. Application to extragalactic sources is of significant appeal, as it would enable a unique and reliable probe of cosmic baryons. We examine temporal power spectra for 3C 84, observed at 1.7 GHz with the Karl G. Jansky Very Large Array and the Robert C. Byrd Green Bank Telescope. These data constrain the ratio between standard deviation and mean intensity for 3C 84 to less than 0.05% at temporal frequencies ranging between 0.1 and 200 Hz. This limit is 3 orders of magnitude below the variability predicted by Lieu & Duan and is in accord with theoretical arguments presented by Hirata & McQuinn rebutting electron density dependence. We identify other spectral features in the data consistent with the slow solar wind, a coronal mass ejection, and the ionosphere.