No precise localization for FRB 150418: claimed radio transient is AGN variability

Abstract

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.

ApJL in press; 7 pages, 3 figures, 2 tables. v2: resubmitted version; v1 was an early arxiv-only note