{
  "bibcode": "2017GCN.21580....1N",
  "body": "M. Nicholl (Harvard), P. S. Cowperthwaite (Harvard), E. Berger (Harvard),\nP. K. G. Williams (Harvard), S. Allam (Fermilab), J. Annis (Fermilab), J.\nGarcia Bellido (IFT CSIC/UAM), D. J. Brout (UPenn), D. Brown (Syracuse), R.\nE. Butler (Fermilab), H.-Y. Chen (Harvard), R. Chornock (Ohio University),\nE. Cook (TAMU), , H. T. Diehl (Fermilab),\nA. Drlica-Wagner (Fermilab), Z. Doctor (U. Chicago), M. R. Drout\n(Carnegie), B. Farr (U Chicago), R. J. Foley (UCSC), W. Fong\n(Northwestern), D. Fox (Penn State), J. Frieman (Fermilab/UChicago), M.S.S.\nGill (Stanford), R. Gruendl (NCSA), K. Herner (Fermilab), D. Holz (UChicago),\nR. Kessler (UChicago), H. Lin (Fermilab), J. Marriner (Fermilab), R.\nMargutti (Northwestern), J. Marshall (TAMU), E. Neilsen (Fermilab), F.\nPaz-Chincon (NCSA), A. Rest (STScI), M. Sako (UPenn), D. Scolnic (KICP), N.\nSmith (Arizona), M. Soares-Santos (BrandeisU), D. Tucker (Fermilab), V. A.\nVillar (Harvard), A. Walker (NOAO), B. Yanny (Fermilab), P. Lopes (UFRJ),\nF. Durret (IAP), A. Louren��o (UFRJ)\n\nOn behalf of the DESGW+community team:\n\nWe report further i- and z-band photometry from DECam imaging of\nthe possible optical counterpart to G298048 first identified in Coulter et\nal. (LVC GCN 21529), and further reported on by Allam et al. (LVC GCN\n21530), Valenti et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532) and\nArcavi et al. (GCN 21538). Observations were obtained on 2017-08-19 at\n23:23 UTC.\n\nWe find preliminary PSF magnitudes of\n\ni = 17.8 +/- 0.1 mag\nz = 17.6 +/- 0.1. mag\n\nIn images obtained the previous night (2017-08-18 at 00:04 UT), we measured\ni ~ z ~ 17.5 mag (Nicholl et al., LVC GCN 21541). This indicates a fading\nof\n~0.3 mag in i-band over the course of 1 day. This value is consistent with\nthat\nexpected for an afterglow or rapidly-evolving kilonova.\n\nThese magnitudes are determined from differential PSF photometry of DECam\nimages relative to Pan-STARRs 3pi catalogs.\n\nFurther analysis is ongoing.",
  "circularId": 21580,
  "createdOn": 1503102143000,
  "email": "pcowperthwaite@cfa.harvard.edu",
  "subject": "LIGO/Virgo G298048: Observed fading of optical counterpart SSS17a",
  "submitter": "Philip Cowperthwaite at Harvard U  <pcowperthwaite@cfa.harvard.edu>",
  "eventId": "LIGO/Virgo G298048"
}