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.
