A search for sub-second radio variability predicted to arise toward 3C   84 from intergalactic dispersion
  We empirically evaluate the scheme proposed by Lieu & Duan (2013) 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 0.1-200 Hz. This limit is 3 orders of magnitude below the variability predicted by Lieu & Duan (2013) and is in accord with theoretical arguments presented by Hirata & McQuinn (2014) 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. 
C. A. Hales (NRAO), W. Max-Moerbeck (NRAO, MPIfR), D. A. Roshi (NRAO),   M. P. Rupen (NRCC)
astro-ph.HE astro-ph.CO astro-ph.SR