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

Abstract

<BR /> 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 the fast radio burst FRB 150418. <BR /> Methods: We observed WISE J0716-19 at 5.0 GHz with the European VLBI Network (EVN) four times between 2016 March 16 and June 2. At three epochs, we simultaneously observed the source with e-MERLIN at the same frequency. <BR /> Results: We detected a compact source in the EVN data in each epoch with a significance of up to ~8σ. The four epochs yielded consistent results within their uncertainties for the peak surface intensity and positions. The mean values for these quantities are I<SUB>peak</SUB> = (115 ± 9)μJy beam<SUP>-1</SUP> and RA = 07<SUP>h</SUP>16<SUP>m</SUP>34.55496(7)<SUP>s</SUP>, Dec = -19°00'39.4754(8)''. The e-MERLIN data provided ~3-5σ detections at a position consistent with those of the EVN data. The emission on angular scales intermediate between the EVN and e-MERLIN is consistent with being null. The brightness temperature of the EVN core is T<SUB>b</SUB> ≳ 10<SUP>8.5</SUP> K, close to the value previously required to explain the short-term radio variability properties of WISE J0716-19 in terms of interstellar scintillation. <BR /> Conclusions: Our observations provide direct and independent evidence of a nuclear compact source in WISE J0716-19, a physical scenario without evident connection with FRB 150418. However, the EVN data do not indicate the variability observed with the VLA.