e-MERLIN, VLBA and Subaru astrometry of the proposed host galaxy of FRB 150418
ATel #8938; C. Bassa (ASTRON), R. Beswick (JBCA), S. J. Tingay (INAF), S. Bhandari (Swinburne), S. Johnston (ATNF), E. F. Keane (SKAO), B. W. Stappers (JBCA), N. Tominaga (Konan) & T. Totani (Tokyo) on behalf of SUPERB and a larger collaboration
on 12 Apr 2016; 18:02 UT
Credential Certification: Evan Keane (ekean@jb.man.ac.uk)
We have obtained e-MERLIN and VLBA observations (observation code BT136) of the radio source associated with FRB 150418 by Keane et al. (2016, Nature, 530, 453), previously detected at low angular resolution (host galaxy WISE J071634.59-190039.2 at z=0.492). With both e-MERLIN and the VLBA we have detected unresolved radio emission from this object at 5 GHz (e-MERLIN 4.8165-5.3285 GHz, VLBA 4.852-5.108 GHz).
With e-MERLIN, the measured peak brightness was 144 uJy/beam on March 22, 2016, at coordinates RA=07:16:34.5550(4); DEC=-19:00:39.466(18): J2000, with an image RMS of 25 uJy/beam. With the VLBA, the peak brightness was 130 uJy/beam on March 8, 2016, at coordinates RA=07:16:34.5550(1); DEC=-19:00:39.480(3): J2000, with an image RMS of 14 uJy/beam. The coordinates derived from the e-MERLIN and VLBA data are in agreement and are consistent with previously reported ATCA (Keane et al.) and VLA (Vedantham et al. 2016, arXiv:1603.04421) coordinates. These detections are also consistent with the non-detection by the EVN reported in ATel #8865.
A 14 arcmin by 14 arcmin subsection of the April 19, 2015 Subaru Suprime-Cam i-band observation of the field containing FRB 150418 was calibrated against astrometric standards from the UCAC4 catalog (Zacharias et al. 2013, AJ, 131, 1163). A total of 78 stars were used, providing RMS position residuals of 101 mas in right ascension and 83 mas declination. Based on this calibration, the centre of the galaxy is at RA=07:16:34.556(7); DEC=-19:00:39.53(8): J2000. On this basis, our astrometry shows that the compact radio source sits at the centroid of WISE J071634.59-190039.2, within the uncertainties quoted above.
Monitoring of WISE J071634.59-190039.2 is ongoing to establish if the compact radio source is associated with the proposed FRB afterglow. Papers describing the detailed astrometry, and the ongoing monitoring of the light curve are in preparation. We encourage continued monitoring of the source in the radio with other telescopes, especially in the L, C and X bands, to allow for cross-calibration. We thank both e-MERLIN and NRAO for providing observations under Director's Discretionary Time.
