{
  "bibcode": "2017GCN.21897....1D",
  "body": "A. Deller (Swinburne/OzGrav), M. Bailes (Swinburne/OzGrav), I. Andreoni\n(Swinburne/OzGrav/AAO), K. Bannister (CSIRO), J. Cooke (Swinburne/OzGrav),\nD. Dobie (University of Sydney), D. Kaplan (UWM), C. Lynch (University of\nSydney), T. Murphy (University of Sydney), on behalf of a joint effort\nbetween OzGrav and the VAST collaboration.\n\n\nWe have further analysed the Very Long Baseline Array (VLBA) observations of\nthe field containing NGC 4993 and SSS17a/DLT17ck (Deller et al., LVC GCN\n21588; Deller et al., LVC GCN 21850), producing images centered on the\nsub-mJy radio source at the centre of NGC 4993 (Alexander et al., LVC GCN\n21545;  Alexander et al., LVC GCN 21548; Bannister et al., LVC GCN 21559;\nAlexander et al., LVC GCN 21589; Corsi et al., LVC GCN 21614).\n\nThe source is detected with a flux density of 0.22 mJy (9 sigma\nsignificance, flux calibration scale uncertainty estimated at 20%).  The\ndata is consistent with either an unresolved or marginally resolved source,\nwhile comparison with the flux densities estimated by the ATCA and VLA\nobservations indicate that most (or possibly all) of the source flux is\ncontained within this milliarcsecond-scale component. Taking the synthesized\nbeam size of 2.5 x 1.0 mas as an upper limit to the source size, the\ninferred lower limit for the brightness temperature is 1.6 x 10^6 K,\nconsistent with an AGN interpretation.  The position obtained is\n13:09:47.69398 -23:23:02.3195 (J2000), with estimated uncertainties\n(dominated by systematics) of <=1 mas in each coordinate.",
  "circularId": 21897,
  "createdOn": 1505807482000,
  "email": "igor.andreoni@gmail.com",
  "subject": "LIGO/Virgo G298048: Milliarcsecond imaging of the NGC 4993 central radio source",
  "submitter": "Igor Andreoni at Swinburne U of Tech  <igor.andreoni@gmail.com>",
  "eventId": "LIGO/Virgo G298048"
}