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

TL;DR

The paper challenges previous claims of precise localization for FRB 150418, arguing that the observed radio transient is likely due to AGN variability rather than a genuine FRB afterglow, thus questioning the association with the proposed host galaxy.

Contribution

It provides evidence that the supposed transient is a variable AGN, not an FRB afterglow, and demonstrates that the localization and redshift claims are not justified.

Findings

The transient is consistent with AGN variability.

The host galaxy shows variability typical of AGN activity.

The proposed transient light curve is better explained by scintillation or AGN flare.

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.