On the nature of FRB 150418: clues to its nature from European VLBI Network and e-MERLIN observations

Aims. We investigate the nature of the compact, and possibly variable nuclear radio source in the centre of WISE J0716􀀀19, the proposed host galaxy of fast radio burst, FRB 150418. Methods. We observed WISE J0716􀀀19 at 5.0 GHz with the European VLBI Network four times between 2016 March 16 and June 2. At three epochs, we simultaneously observed the source with e-MERLIN at the same frequency. Results. We detected a compact source in the EVN data in each epoch with a significance up to 8. The four epochs yielded consistent results within their uncertainties, for both peak surface intensity and positions. The mean values for these quantities are Ipeak = (115 9) Jy beam􀀀1 and r.a. = 07h 16m 34.55496(7)s, dec. = 􀀀19 000 39.4754(8)00, respectively. The e-MERLIN data provided 3 􀀀 5 detections, at a position consistent with those of the EVN data. The presence of emission on angular scales intermediate between the EVN and e-MERLIN is consistent with being null. The brightness temperature of the EVN core is Tb & 108:5K, close to the value required by Akiyama & Johnson (2016) to explain the radio properties of WISE J0716􀀀19 in terms of interstellar induced short-term variability. Conclusions. Our observations provide direct, independent evidence of the existence of a nuclear compact source in WISE J0716􀀀19, a physical scenario with no evident connection with FRB 150418. However, the EVN data do not show indication of the variability observed with the VLA.