Final results of VLA monitoring of the FRB 150418 host galaxy candidate spanning 35 days

ATel #8946; P. K. G. Williams (CfA), E. Berger (CfA)
on 13 Apr 2016; 17:45 UT
Credential Certification: Peter Williams (peter@newton.cx)

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The z ~ 0.5 galaxy WISE J071634.59-190039.2 has been proposed as the host of a radio transient associated with FRB 150418 (Keane et al., 2016 Nature 530 453). We previously reported a detection of a rebrightening in VLA follow-up observations (program VLA/16A-431; ATel #8752) and a more extended light curve showing persistent variability (Williams & Berger, 2016 ApJL in press; arxiv:1602.08434). Here we report four additional epochs of data that complete our follow-up program, spanning a total of 35 days:

 
MJD | 5.5 GHz flux density (mJy) | 7.5 GHz flux density (mJy) 
 
57470.97 | 185 +- 18 | 83 +- 20 
57475.96 | 259 +- 21 | 152 +- 18 
57478.98 | 205 +- 15 | 156 +- 18 
57479.93 | 260 +- 34 | 259 +- 42 

An updated version of Figure 1 from Williams & Berger (2016), showing the complete VLA light curve, is available at the URL linked below. Combining the large and persistent flux density variations, which are similar in amplitude and timescale to the original variation seen in the ATCA data, with observations of a flat broadband spectrum (Vedantham et al. 2016, arXiv:1603.04421) and a VLBI unresolved compact radio core (ATel #8938) leads to the conclusion that the source of variable radio emission is AGN variability (e.g. Akiyama & Johnson, arxiv:1603.04880) and not an afterglow associated with FRB 150418 (see Williams & Berger, 2016, for more detailed and expanded arguments).

We note that an EVN non-detection (<170 uJy/bm, 6 sigma; ATel #8865) reported just before our March 16th observation (Williams & Berger, 2016) possibly indicates a rapid rise in the compact source's flux density around MJD 57463.9.

To facilitate comparison of data sets, proprietary restrictions on the VLA data will be released shortly.

Full VLA light curve, updating Williams & Berger (2016 ApJL in press)