{
  "bibcode": "1999GCN...300....1V",
  "body": "The U.S. Naval Observatory GRB team (F.J. Vrba, A.A. Henden, C. B.\nLuginbuhl, B. Canzian, S.E. Levine, H.H. Guetter, J.A. Munn), D.H.\nHartmann (Clemson Univ.), M.C. Jennings (IGPP, UCR visitor), and A.J.\nCastro-Tirado (LAEFF-INTA, IAA-CSIC, Spain),  M.R. Zapatero-Osorio, R.\nCasas, V. Motta (IAC, Spain), J. Gorosabel (LAEFF-INTA), and J. Greiner\n(AIP, Germany)\n\nreport a second night of calibrated photometric observations of the GRB\n990506 field, obtained at the U.S. Naval Observatory, Flagstaff Station\nwith the 1.0-m reflector.  Observations in B, V, R(Cousins), and\nI(Cousins) using a CCD with an 11x11 arcmin field were centered\napproximately at the center of the intersection of the IPN3 (GCN 291)\nand the revised RXTE x-ray localization (of UT 1999 May 07 02:31:42).\nDeep Rc-band images formed from 12 stacked 10-minute exposures were\nobtained on both nights.  No clearly variable object within the IPN\nannulus was seen, down to a detection limit of roughly Rc=23.\n\nOne object 1.6 arcmin outside the revised IPN annulus (GCN 298) but\nwithin the revised RXTE localization (GCN/RXTE_PCA Burst Position\nNotice of 990507 02:31:42 UT) appears to be variable, fading from\napproximately Rc=22.0 (+/- 0.2mag) on 990507 UT to below our detection\nlimit on 990508 UT.  The coordinates of this object are 11:54:57.80,\n-26:43:03.8 (J2000, +/- 0.2 arcsec).  A 2.7 arcmin square finding chart\n(NE = upper left) for this object can be found on\n  ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb990506.gif\n\nThe BVRcIc photometric calibration file in this directory\n(grb990506.dat) will be revised in the near future to reflect the\nsecond night of all-sky photometry.\n\nThis GCN note can be cited.",
  "circularId": 300,
  "createdOn": 926156206000,
  "email": "aah@nofs.navy.mil",
  "subject": "GRB 990506, optical observations",
  "submitter": "Arne A. Henden at USNO/USRA  <aah@nofs.navy.mil>",
  "eventId": "GRB 990506"
}