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Radio brightening of FRB 150418 host galaxy candidate

ATel #8752; P. K. G. Williams (CfA), E. Berger (CfA), R. Chornock (Ohio Univ.)
on 29 Feb 2016; 05:26 UT
Credential Certification: Peter Williams (peter@newton.cx)

Subjects: Radio, AGN, Variables

Referred to by ATel #: 8865, 8946, 8959

Keane et al. (2016 Nature 530 453) reported a fading radio transient in the z=0.498 galaxy WISE J071634.59-190039.2 (WISE 0716-19; Williams & Berger, arxiv:1602.08434) that they associated with the fast radio burst FRB 150418. We conducted two 1.5-hr VLA observations of WISE 0716-19 at mean MJDs 57445.06 and 57446.04 (UT 2016 Feb 27/28; program VLA/16A-431), observing in a 5-6 GHz bandpass and using 3C 147 as the flux density calibrator, referencing to the Perley & Butler (2013 ApJS 204 19) flux density scale. After standard flagging and analysis, we detect an unresolved source at the position of WISE 0716-19 with a mean flux density of 0.157 +- 0.006 mJy/bm at 5.50 GHz and a negative spectral index (alpha ~= -0.8, S_nu ~ nu^alpha); the synthesized beam shape was 9" x 3". No clear evidence of variability is seen. The flux density is 3.3 sigma higher than the average of the steady measurements reported by Keane et al., 0.097 +- 0.012 mJy/bm, suggesting that the claimed transient is instead a variable radio source. We therefore argue that claimed localization of FRB 150418 to WISE 0716-19 is invalid (cf. Williams & Berger, arxiv:1602.08434). Additional observations and analysis are ongoing.