{
  "bibcode": "2017GCN.20398....1K",
  "body": "M. M. Kasliwal (Caltech), L. P. Singer (NASA/GSFC), E. Karamehmetoglu\n(OKC),  S. B. Cenko (NASA/GSFC), R. Quimby (SDSU), D. Cook (Caltech), T.\nBarlow (Caltech), V. Bhalerao (IUCAA), J. Rana (IUCAA), A. Goobar (OKC), J.\nSollerman (OKC), R. Amanullah (OKC), Y. Cao (UW Seattle), A. A. Miller\n(Northwestern/Adler)\n\nreport on behalf of the iPTF and GROWTH collaborations:\n\nWe have performed tiled observations of LIGO/Virgo G268556 (LVC, GCN 20364)\nusing the Palomar 48-inch Oschin telescope (P48). Due to weather, our\nobservations only began on 2017-01-07 UTC. The northern probability island\nfrom the updated LALInference localization (LVC, GCN 20385) was observable\nfrom Palomar for most of the night. Starting at 13:03 UT (2.88 d after the\nLIGO trigger), we imaged 85 of the fields two or more times, spanning 622\nsquare degrees. We estimate a 32% prior probability that these fields\ncontain the true location of the source.\n\nDuring preliminary sifting through candidate variable sources using image\nsubtraction by both our IPAC pipeline (Masci et al. 2016) and NERSC\npipeline (Cao et al. 2016), and applying standard iPTF vetting procedures,\nwe flagged the following optical transient candidates for further follow-up:\n\n  name       RA        Dec      time  mag    z     notes\n-------- ---------- ---------- ----- ----- ------ ---------\niPTF17bo 132.510142 +46.663565 06:13 18.57 0.038   =ATLAS16ecj (GCN 20377)\niPTF17bq 132.192751 +44.006807 06:11 19.11 0.054   spec-z\niPTF17bs 128.827313 +44.022911 06:11 20.35 0.049   photo-z\niPTF17bt 130.174781 +39.306960 06:08 20.05 0.1166  spec-z\niPTF17bu 124.471393 +40.726652 06:06 20.69 0.0608  spec-z\niPTF17bv 124.186115 +41.266753 06:06 19.23 0.039   spec-z\niPTF17cc 125.336819 +35.420771 06:00 20.06 0.064   spec-z\niPTF17ce 122.265555 +24.773640 05:55 20.19 0.350   photo-z\niPTF17cf 122.967123 +25.422642 05:55 19.06 0.199   photo-z\niPTF17ch 123.698029 +27.836746 05:53 20.22 0.118   photo-z\niPTF17ck 115.465769 +29.353904 07:08 19.18 0.169   photo-z\niPTF17cp 115.146554 +17.018280 07:05 19.90 0.072   spec-z\niPTF17cs 115.613615 +13.805968 07:03 19.48 0.066   photo-z\niPTF17cv 114.643374 +23.994179 07:01 20.60 0.081   photo-z\niPTF17dk 120.728531 +16.489364 07:21 20.00 0.069   photo-z\niPTF17dn 115.013574 +13.340217 09:11 19.08 0.037   photo-z\niPTF17du 114.886641 +10.661666 07:15 20.05 0.412   photo-z\niPTF17dz 126.106981 +24.997750 09:40 19.33 0.235   photo-z\niPTF17eb 118.169444 +10.174427 09:20 19.78 0.573   photo-z\niPTF17ec 111.440505 +17.716475 09:13 19.50         no redshift available\niPTF17ee 146.552954 +60.363235 10:07 19.15 0.102   possibly variable\niPTF17ef  117.10532 +20.863792 07:06 20.32 0.162   photo-z\niPTF17eh 116.453873  +9.318206 07:15 19.75 0.077   photo-z\niPTF17ei 114.113854 +25.736748 09:29 19.56 0.101   photo-z\niPTF17ej 116.903063 +25.599466 09:29 20.40 0.543   photo-z\niPTF17ep 137.758943 +62.963989 09:38 19.97 0.115   photo-z\niPTF17et  126.46248 +32.611008 07:30 19.46 0.124   spec-z\niPTF17ez 118.434093 +19.300562 07:14 20.19 0.538   photo-z\niPTF17fa 130.091957 +38.723745 06:08 19.94 0.673   photo-z\niPTF17fb 123.253486 +41.307429 06:06 20.38 0.282   photo-z\niPTF17fc 123.845936 +40.118490 06:04 19.78 0.067   photo-z\n\nSome additional transients not listed above fell just outside the 90%\ncontour localization contour, e.g. iPTF17cw 135.909904 +43.097300.\n\nPositions are stated in the ICRS. Times are in UTC. Magnitudes are based on\nimage subtraction; they are in the Mould R filter and in the AB system,\ncalibrated with respect to point sources in SDSS as described in Ofek et\nal. 2012.\n\nNone of the above transients show prior history of detection in iPTF\narchival images. All of the above transients coincide with a galaxy that is\nvisible in iPTF and/or SDSS images. Archival spectroscopic or photometric\nredshifts of the transients' likely host galaxies are given above. Of the\ntransients, those that are most consistent with the directional distance\nestimate from LIGO (e.g., |[galaxy distance] - [GW mean distance]| < 1.5 *\n[GW distance std.\ndev.]) are iPTF17ce, iPTF17ck, iPTF17dz, iPTF17ef, and iPTF17ei.\n\nWe encourage spectroscopic classification of these candidates.",
  "circularId": 20398,
  "createdOn": 1483844277000,
  "email": "mansi@astro.caltech.edu",
  "subject": "LIGO/Virgo G268556: iPTF Optical Transient Candidates",
  "submitter": "Mansi M. Kasliwal at Caltech  <mansi@astro.caltech.edu>",
  "eventId": "LIGO/Virgo G268556"
}