No precise localization for FRB 150418: claimed radio transient is AGN
  variability
  Keane et al. have recently claimed to have obtained the first precise
localization for a Fast Radio Burst (FRB) thanks to the identification of a
contemporaneous fading slow (~week-timescale) radio transient. They use this
localization to pinpoint the FRB to a galaxy at z ~ 0.49 that exhibits no
discernable star formation activity. We argue that the transient is not genuine
and that the host candidate, WISE J071634.59-190039.2, is instead a radio
variable: the available data did not exclude this possibility; a random radio
variable consistent with the observations is not unlikely to have a redshift
compatible with the FRB dispersion measure; and the proposed transient light
curve is better explained as a scintillating steady source, perhaps also
showing an active galactic nucleus (AGN) flare, than a synchrotron-emitting
blastwave. The radio luminosity of the host candidate implies that it is an AGN
and we present new late-time Very Large Array observations showing that the
galaxy is indeed variable at a level consistent with the claimed transient.
Therefore the claimed precise localization and redshift determination for FRB
150418 cannot be justified.
