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e-EVN measurement of the FRB 150418 host galaxy candidate

Submitter: Zsolt Paragi
Description: Earlier this year, Keane et al. (2016) announced the discovery and accurate localization of a rare type of transient signal called a Fast Radio Burst (FRB), that lasts only for a few milliseconds. The origin of FRBs is not clear yet, but they are likely located at great distances from us, at least in neighbouring galaxies or even further away. Keane et al. have developed a real-time transient detection system at Parkes Observatory, and detected FRB 150418 last year. Surveying the area with the Australia Telescope Compact Array (ATCA) revealed an 'afterglow' signal that faded away in 6 days. This variable source was located in a galaxy at a redshift of z=0.492. If the FRB and the fading radio source seen by ATCA are related, this means that at least some of the FRBs are truly cosmological (see AJDI 20160226 by Emily Petroff).

There were, however, claims that the two events are not related. According to Williams & Berger (2016), Very Large Array (VLA) monitoring results show that there is a highly variable radio source in the centre of the claimed host galaxy of FRB 150418, a source that they interpret as an active galactic nucleus (AGN). The short timescale variability implies that the AGN must be very compact.

To probe the nuclear radio emission of the proposed host galaxy, we carried out very long baseline interferometer (VLBI) observations with the e-EVN at 5 GHz, on 2016 March 16. These data confirm a nuclear radio source compact on milliarcsecond scales in the host galaxy WISE J071634.59-190039.2, and therefore the existence of an AGN. The peak brightness of the emission was just 127 microJy/beam, consistent with other high resolution observations. Further observations with the EVN are planned, and a comparison with other projects carried out with VLA, ATCA, VLBA, and e-MERLIN, is expected to clarify important details about the nature of this radio source, and in particular its association with the FRB. The results were reported by Marcote et al. in ATel #8959. The e-EVN image above was provided by Marcello Giroletti (INAF).
Copyright: Astron/JIVE
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