{
  "bibcode": "2016GCN.19760....1S",
  "body": "L. P. Singer (NASA/GSFC), M. M. Kasliwal (Caltech), Varun Bhalerao (IUCAA),\nAnna Ho (Caltech), Tom Barlow (Caltech), S. B. Cenko (NASA/GSFC),\nE. O. Ofek (Weizmann), N. Strotjohann (DESY), A. Franckowiak (DESY),\nM. Kowalski (DESY), and G. Tesic (PSU) report on behalf of the\nIntermediate Palomar Transient Factory (iPTF) collaboration:\n\nFollowing the detection and updated localization of the cosmic neutrino\ncandidate IceCube-160731A\n(http://gcn.gsfc.nasa.gov/notices_amon/6888376_128290.amon), we began\nsearching for optical counterparts using the Palomar 48-inch Oschin\ntelescope (P48) on 2016-07-31 at 05:22 UT, 3.5 hours after the trigger.\n\nWe imaged one field covering an area of 7.1 deg^2 to a limiting magnitude\nof R=19.1--19.7. Unfortunately, the EHE localization coincides with an\ninoperable CCD. Sifting through candidate variable sources using image\nsubtraction and standard iPTF vetting procedures, we do not detect any\noptical transients close to the IceCube error circle. Two optical\ntransient candidates are found at 1.1 and 2.0 deg from the neutrino\ncandidate position:\n\n   name       RA        Dec     sep  mag   t\n-----------------------------------------------\niPTF16elf 213.555124 -0.894361 1.1 17.25 3.5\niPTF16elg 212.640918 -0.988094 2.0 18.71 3.75\n\nThe two transients are positionally consistent with the nuclei of their\nrespective host galaxies, CGCG 018-088 at z=0.038 and SDSS\nJ141033.84-005918.0 at z=0.054.\n\nPositions are in J2000. Separations are in degrees and relative to the\nbest-estimate IceCube position (214.5440d -0.3347d). Magnitudes are in the\nMould R filter and in the AB system, calibrated with respect to point\nsources in SDSS as described in Ofek et al. (2012,\nhttp://dx.doi.org/10.1086/664065). Times are in hours since the IceCube\ntrigger.\n\nThe diagram http://asd.gsfc.nasa.gov/Leo.Singer/iptf/IceCube-160731.pdf\nshows the P48 field in relation to the IceCube 1-sigma error circles.",
  "circularId": 19760,
  "createdOn": 1470269498000,
  "email": "leo.p.singer@nasa.gov",
  "subject": "IceCube-160731A: iPTF P48 Observations",
  "submitter": "Leo Singer at GSFC/iPTF  <leo.p.singer@nasa.gov>",
  "eventId": "IceCube-160731A"
}