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

¹ INAF Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
e-mail: giroletti@ira.inaf.it
² Joint Institute for VLBI ERIC, Postbus 2, 7990 AA Dwingeloo, The Netherlands
³ Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁴ Department of Earth and Space Sciences, Chalmers University of Techn., Onsala Space Observatory, 43992 Onsala, Sweden
⁵ Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588, Japan
⁶ Jodrell Bank Centre for Astrophysics/e-MERLIN, The University of Manchester, M13 9PL, UK
⁷ Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352, USA

Received: 23 June 2016
Accepted: 5 September 2016

Abstract

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.

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.

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_peak = (115 ± 9)μJy beam^-1 and RA = 07^h16^m34.55496(7)^s, 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_b ≳ 10^8.5 K, close to the value previously required to explain the short-term radio variability properties of WISE J0716−19 in terms of interstellar scintillation.

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.