{
  "bibcode": "2017GCN.21262....1S",
  "body": "K. W. Smith, K. C. Chambers (IfA), M. E. Huber (IfA), S. J. Smartt,\nT.-W. Chen (MPE), M. Coughlin (Harvard), D. E. Wright, D. R. Young,\nE. Kankare (QUB), H. Flewelling, T. Lowe, E. A. Magnier,\nA. S. B. Schultz, C. Waters, R. J. Wainscoat, M. Willman\n(IfA),J. Tonry, L. Denneau, A. Heinze, B. Stalder, H. Weiland (IfA),\nC. W. Stubbs (Harvard), A. Rest (STScI),\n\n\nGCN 21227 (Omedi et al.) reported detection of a weak gamma-ray\ncandidate with Fermi/lAT at position R.A.,Dec.=128.11, 43.39, (J2000)\nwith a localization error of 0.24 degree, which is within the skymap\nof the LIGO GW Binary Merger Candidate G288732 (GCN 21221, Becsy et\nal.), discovered at 2017-06-08 02:01:16.492 UTC (57912.08421866)\n\nWe report that we observed the Fermi/LAT postion with the Pan-STARRS1\ntelescope (Chambers et al. arXiv:1612.05560). We began taking data at\n2017-06-09T 06:03:40 UT, centered on the Fermi position with a set of\n8 dithered exposures in i and z band filters. The PS1 camera \nencloses a circle of 2.9 degree diamater, and therefore enclosed the \nwhole of the Fermi/LAT error box. \n\nDifference images were produced by subtracting the Pan-STARRS1 3Pi\nreference image from these separate exposures and a nightly combined\nstack of the dithers (3Pi data described in Chambers et\nal. arXiv:1612.05560, and available at http://panstarrs.stsci.edu).\nUsing techniques discussed in Smartt et al. (2016, MNRAS, 462, 4094),\nwe located and vetted transients with quality filters and a machine\nlearning algorithm on the difference images.\n\nNo fast evolving transients (with variable lightcurves) were found\nduring the first night of data (MJD ~ 57913.25 to 57913.30) in the\nindividual 240s exposures, with limits of z > 18.5 +/- 0.5 (given the\nairmass range of 1.9 - 2.8 and poor image quality).\n\nThree transients were found in the stacked data covering several \nnights between 57913 and 57924. However all three are outside the\nerror radius of 0.24 degrees from Fermi/LAT. In summary, no possible\noptical counterpart to the Fermi/LAT source is detected to \ni,z ~ 18.5 (within 24hrs) and i,z ~ 20.5 (daily stacked limits up to \n5 days after). \n\nThe detected sources are below (where AngSep = angular separation\nfrom the Fermi/LAT position in degrees)  \n\nName      RA (J2000)   Dec (J2000)  Disc. MJD  Disc Mag    AngSep \nPS17diu   08 35 24.13  +44 00 29.5  57913.26    18.82 (z)  0.82\nPS17dit   08 27 39.44  +42 36 36.2  57916.28    20.56 (i)  0.78\nPS17djl   08 30 31.25  +43 55 04.2  57916.29    20.45 (i)  0.63\n\nPS17diu is associated with SDSS J083524.25+440029.3, an r=19.36 mag\ngalaxy with a host photoZ=0.083 (+/- 0.038) implying a transient M_i =\n-19.36. The lightcurve is relatively flat over 10 days. This is likely\nan old SN, and this is likely an old SN around peak.\n\nPS17dit is likely associated with 2MASX J08273960+4236311; a 18.50 mag\ngalaxy with z=0.151, implying a transient at M = -18.8. The lightcurve\nis flat for 4 days, and this is likely an old SN around peak.\n\nPS17djl is likely associated with SDSS J083031.05+435504.3; an r=19.81\nmag galaxy with A host photoZ=0.217 (+/- 0.051) implying a transient\nat M = -19.7. Again, the lightcurve is flat for 4 days, also\nsuggesting this is likely an old SN around peak.",
  "circularId": 21262,
  "createdOn": 1498147865000,
  "email": "s.smartt@qub.ac.uk",
  "subject": "LIGO/Virgo G288732: Pan-STARRS coverage of the Fermi/LAT candidate position",
  "submitter": "S. J. Smartt at Queens U Belfast  <s.smartt@qub.ac.uk>",
  "eventId": "LIGO/Virgo G288732"
}