{
  "bibcode": "2017GCN.20790....1K",
  "body": "M. M. Kasliwal (Caltech), S. M. Adams (Caltech), C. Cannella (Caltech), R.\nLunnan (Caltech), R. Ferretti (OKC), T. Kupfer (Caltech), L. P. Singer\n(NASA/GSFC), S. B. Cenko (NASA/GSFC), R. Walters (Caltech), T. Barlow\n(Caltech), J. Rana (IUCAA), V. Bhalerao (IIT-B), A. A. Miller\n(Northwestern/Adler), Y. Cao (UW), R. Laher (IPAC), F. Masci (IPAC)\n\nreport on behalf of the iPTF (intermediate Palomar Transient Factory) and\nGROWTH (Global Relay of Observatories Watching Transients Happen)\ncollaborations:\n\nWe performed tiled observations of LIGO/Virgo G275404 (LVC, GCN 20738) and\nLIGO/Virgo G275697 (LVC, GCN 20763) using the Palomar 48-inch Oschin\ntelescope (P48) on the night of 2017-03-01 UTC (delay due to inclement\nweather). We imaged 84 fields spanning 633 square degrees, with a 17%\nchance of containing the true location of G275404. Of these, 47 fields (361\nsquare degrees) were imaged twice, containing 11% of the probability of\ncontaining G275404, and searched for transient candidates.\n\nDuring preliminary sifting through candidate variable sources using image\nsubtraction by our IPAC (Masci et al. 2016) and NERSC (Cao et al. 2016)\npipelines, a total of 140 candidates were saved in the fields imaged.\nApplying standard iPTF vetting procedures and removing transients with a\nhistory of previous variability, we flagged 27 optical transient candidates\nin the 90% localization contour of G275404, listed below, for further\nfollow-up.\n\nName         RA              Dec            UTC          R-mag      z\nNotes\niPTF17bpa   150.966591      1.095135        09:07        18.72   0.0456\nspecz; off center from host\niPTF17bpb   154.902074      -2.992951       09:25        19.56   0.0511\nphotz; pstar=0.016; nuclear?\niPTF17bpc   155.671912      -3.647882       09:25        19.31\npstar=0.001; nuclear?\niPTF17bpd   155.181672      -4.163867       09:25        19.28\npstar=0.804; nuclear/stellar?\niPTF17bpk   157.626592      -11.121047      10:20        19.63\nnuclear/stellar?\niPTF17bpm   161.324311      -14.376753      10:04        19.26\npstar=0.229; nuclear/stellar?\niPTF17bpn   161.238427      -14.017486      10:04        19.56\npstar=0.46; nuclear/stellar?\niPTF17bpo   158.494163      -12.65084       10:02        19.03\npstar=0.96; nuclear/stellar?\niPTF17bps   161.952768      -15.243493      10:04        19.76\nhostless (very slow mover?)\niPTF17bpt   157.657157      -7.372908       09:29        19.49\nfading (0.5 mag intra-night); pstar=0.89; nuclear/stellar?\niPTF17bpu   157.559861      -6.799173       09:29        19.81\npstar=0.612; nuclear/stellar?\niPTF17bpy   156.687516      -7.684226       09:29        19.98\npstar=0.933; nuclear/stellar?\niPTF17bqc   158.470076      -11.493302      10:02        19.62\npstar=0.717; nuclear/stellar?\niPTF17bqh   156.749276      -10.358467      10:00        19.49\nrising (0.4 mag intra-night); nuclear/stellar?\niPTF17bqi   156.87908       -7.04181        09:29        19.41\npstar=0.962; nuclear/stellar?\niPTF17bqk   162.188261      -15.49746       10:04        19.76\nnuclear/stellar?\niPTF17bqz   157.651689      -7.696641       09:29        19.83\npstar=0.885; nuclear/stellar?\niPTF17bro   288.344596      58.81211        10:59        19.82\nrising (0.5 mag intra-night), nuclear?\niPTF17brp   291.671757      79.220007       11:47        19.42   0.076\nphotz; pstar=0.056; off center from host galaxy\niPTF17brr   289.432632      79.995864       11:47        19.88\npstar=0.898; nuclear/stellar?\niPTF17bru   294.594305      63.706556       11:36        19.95          off\ncenter from host galaxy\niPTF17bsd   156.642225      -10.970993      10:00        19.68\nrising (0.3 mag intra-night); nuclear\niPTF17bsi   297.077103      78.352918       12:01        19.08   0.014\nphotz; off center from host galaxy\niPTF17bst   156.998904      -7.216924       09:29        19.87\npstar=0.973; nuclear/stellar?\niPTF17btb   302.938179      72.930472       12:03        18.56\nnuclear/stellar?\niPTF17btc   309.740925      72.580678       12:03        18.97\nnuclear/stellar?\niPTF17bth   307.33055       68.241724       12:05        19.31\nnuclear/stellar?\n\nPositions are stated in the ICRS. Discovery times are noted in UTC hh:mm on\n2017-03-01. Magnitudes are based on image subtraction and in the Mould R\nfilter, calibrated with respect to point sources in SDSS as described in\nOfek et al. 2012.\n\nWe caution that many candidates are outside the SDSS footprint and lack a\nsecure star/galaxy classification for the underlying source. We flag these\nas \"nuclear/stellar?\". Where available, we provide machine-learning\nprobability scores on whether the underlying source is a galaxy/star (0/1)\n(Miller et al. 2016).\n\nWe encourage spectroscopic classification of these candidates. In\nparticular, we highlight iPTF17bpt, iPTF17bqh, iPTF17bsd as fast-evolving\nby more than 0.3 mag in the same night; iPTF17bpa and iPTF17bsi as local\ntransients (d < 200 Mpc), and iPTF17bpa and iPTF17btb as bright transients\n(m < 19 mag).\n\nWe are grateful to the Palomar crew (especially John Henning, Jeff\nZolkower, Carolyn Heffner, Jamey Eriksen, Nick Ganciu) for their hard work\nin reviving a faulty declination encoder essential to collecting this\ndataset during the last two days of iPTF survey operations.",
  "circularId": 20790,
  "createdOn": 1488439755000,
  "email": "mansi@astro.caltech.edu",
  "subject": "LIGO/Virgo G275404: iPTF Optical Transient Candidates",
  "submitter": "Mansi M. Kasliwal at Caltech  <mansi@astro.caltech.edu>",
  "eventId": "LIGO/Virgo G275404"
}