{
  "subject": "LIGO/Virgo G274296:  ATLAS confirmation of the bright MASTER transient and earlier explosion date",
  "eventId": "LIGO/Virgo G274296",
  "bibcode": "2017GCN.20713....1S",
  "createdOn": 1487690093000,
  "circularId": 20713,
  "submitter": "S. J. Smartt at Queens U Belfast  <s.smartt@qub.ac.uk>",
  "email": "s.smartt@qub.ac.uk",
  "body": "S. J. Smartt, K. W. Smith, D. R. Young, (QUB), J. Tonry, L. Denneau,\nA. Heinze, B. Stalder, H. Weiland (IfA), C. W. Stubbs (Harvard),\nA. Rest (STScI), K. C. Chambers (IfA), T.-W. Chen (MPE), M. Coughlin\n(Harvard), M. E. Huber (IfA), D. E. Wright (QUB), H. Flewelling,\nT. Lowe, E. A. Magnier, A. S. B. Schultz, C. Waters, R. J. Wainscoat,\nM. Willman (IfA)\n\nLipunov et al. (GCN 20712) reported the discovery of a very bright,\nmag=15.7 transient in the sky localisation map of G274296 (GCN20689)\nat the position : \n\nMASTER OT J105519.53+365834.1 RA(2000)=10h 55m 19.53s +36d 58m 34.1s  \n\nat 2017-02-18 18:18:18 UT (MJD=57802.76271) \n\nand close to (within 1.7���) of the centre of an edge-on spiral galaxy\nat z = 0.043224 (KUG 1052+372; PGC 032819)\n\nWith the ATLAS telescope system (see Tonry et al. GCN 20382 and\nwww.fallingstar.com), we confirm the reality of this bright transient,\nhowever it exploded well before the GW detection G274296.  The MJD of the\nGW source was 57801.2541094 as announced in GCN20689.\n\nIn ATLAS routine survey mode we detect the transient (internally called\nATLAS17bbp) on two images on the night of MJD=57794 at mag = 18.23\n(orange filter) and again on 5 images on each of 57798 and 57802, the\nlatest with m=17.40 +/- 0.07 (the orange bandpass is approximately\nequivalent to o ~ 0.56r+0.44i).\n\nThe difference in the magnitudes between ATLAS and MASTER is likely\ndue to ATLAS performing difference imaging photometry and the transient being\nlocated close to the galaxy core.\n\nThe ATLAS17bbp coordinates are RA=163.83115 DEC=+36.97640\n(10:55:19.47 +36:58:35.0)\n\nWhile this is certainly real, and within the LIGO localisation banana,\nit has an explosion date at least 7 days before G274296.  We measure a\n1.2\" difference in the astrometric coordinates of PGC 032819 and\nATLAS17bbp, but further analysis is required to determine if it\nactually is coincident with the galaxy nucleus.\n\nThe source fell outside the northern egde of the Pan-STARRS1 coverage\n(Chambers et al. GCN 20699)."
}