{
  "bibcode": "1999GCN...294....1V",
  "body": "The U.S. Naval Observatory GRB team (F.J. Vrba, A.A. Henden, B. Canzian, \nC.B. Luginbuhl, S.E. Levine, H.H. Guetter, J.A. Munn), D.H. Hartmann\n(Clemson Univ.), M.C. Jennings (IGPP, UCR visitor), and A.J. Castro-Tirado \n(LAEFF-INTA, IAA-CSIC, Spain),  M.R. Zapatero-Osorio, R. Casas,  \nV. Motta (IAC, Spain), J. Gorosabel (LAEFF-INTA), and J. Greiner (AIP, Germany)\nreport observations of the GRB 990506 field, obtained at the U.S. Naval Observatory, \nFlagstaff Station with the 1.0-m reflector. Observations in B, V, R(Cousins), \nand I(Cousins) using a CCD with an 11x11 arcmin field were centered approximately\nat the center of the intersection of the IPN3 (GCN 291) and the revised RXTE\nx-ray localization (of UT 1999 May 07 02:31:42) and thus cover an area several \ntimes the size of this intersection. A series of local standards covering this \nfield and based on all-sky photometry was established and preliminary photometric \nvalues, with +/- 0.05 mag uncertainty to V = 18.5, are available at \nftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb990506.dat, along with astrometry \naccurate to approximately 0.1 arcsec. The RXTE/IPN3 locus was inspected for objects \nwhich had visually different brightness than on the Digital Sky Survey (DSS). \nOne object, located near the center of this intersection at R.A. = 11:54:52.92, \nDEC = -26:43:39.9 (+/- 0.2 arcsec in both coordinates)(J2000), was notably absent \nfrom the DSS image. However, at V = 21.0, V-R = 1.6 (+/- 0.2) its apparently red \ncolor (if not due to variability) might be why it is not visible on the DSS. \nAs of the time of this writing, observations are continuuing in order to determine\nif this object is variable. \n\nThis GCN note can be cited.",
  "circularId": 294,
  "createdOn": 926057930000,
  "email": "fjv@nofs.navy.mil",
  "subject": "GRB 990506, optical observations",
  "submitter": "Fredrick J. Vrba at USNO  <fjv@nofs.navy.mil>",
  "eventId": "GRB 990506"
}