{
  "bibcode": "2017GCN.21886....1T",
  "body": "J. Tonry (IfA), K. W. Smith (QUB), L. Denneau, A. Heinze, B. Stalder,\nH. Weiland (IfA), C. W. Stubbs (Harvard), S. J. Smartt (QUB), A. Rest\n(STScI), K. C. Chambers (IfA), T.-W. Chen (MPE), M. Coughlin\n(Harvard), D. R. Young, (QUB), M. E. Huber (IfA), D. E. Wright (QUB),\nH. Flewelling, T. Lowe, E. A. Magnier, A. S. B. Schultz, C. Waters, R.\nJ. Wainscoat, M. Willman (IfA)\n\n\nDuring its normal survey mode, the ATLAS survey project (Tonry et al.\n2011, Stalder et al. 2017) frequently observed the field containing\ngalaxy NGC4993 during the period between 57380.64463 and 57966.26370\n(602 to 16 days before G298048; the LIGO Scientific Collaboration and\nthe Virgo Collaboration GCN 21509) and the first discoveries and\ndetections of the optical/NIR transient SSSa17a/DLT17ck (Coulter et\nal. GCN 21529, Allam et al. GCN 21530,Valenti et al. GCN21531,\nMelandri et al. 21532).\n\nWe have completed a search for variability or eruptions at the\nposition of the optical transient in the 414 images over this period.\nThese images were taken typically with 4-5 images per night (30 second\nexposures).\n\nATLAS observes in two wide-band filters, called \"cyan\" or \"c:, which\nroughly covers the SDSS/Pan-STARRS g and r filters, and ���orange��� or\n\"o\", which roughly covers the SDSS/Pan-STARRS r and i. The position\nwas observed 414 times in one or other filter and on each of these we\nforced flux measurements at the astrometric position of the transient\non the difference image. We used the Pan-STARRS images for the\nastrometric postion of SSS17a/DLT17ck (Chambers et al. GCN 21553)\n\nWe measured 5-sigma flux limits and any epochs with greater than\n5-sigma detections. The 5-sigma flux limits were in the range 18.5 +/-\n0.4 (AB mag, median and standard deviation) and (19.4 +/- 0.4). We\nfound 44 images which formally had flux detections greater than\n5-sigma, but on visual inspection we rule out these being real flux\nvariability at the transient position. They all appear to be residuals\nfrom the host galaxy subtraction. With ATLAS, we rule out any\nvariability down to 18.5 to 19.4 (filter dependent) during a period\n601 to 16 days before discovery of the optical transient. The last\nimage was on 57966.26370 (2017-08-01 06:19) with a 5-sigma limit of \no < 18.2.",
  "circularId": 21886,
  "createdOn": 1505474655000,
  "email": "s.smartt@qub.ac.uk",
  "subject": "LIGO/Virgo G298048:  ATLAS pre-discovery limits 601 to 16 days before first detection of SSS17a/DLT17ck",
  "submitter": "S. J. Smartt at Queens U Belfast  <s.smartt@qub.ac.uk>",
  "eventId": "LIGO/Virgo G298048"
}