{
  "bibcode": "2002GCN..1503....1H",
  "body": "A. Henden (USRA/USNO) reports on behalf of the USNO GRB team:\n\nWe have acquired UBVRcIc all-sky photometry for\nan 11x11 arcmin field centered at the optical transient coordinates\nfor GRB020813 (Villasenor et al. GCN 1471; Fox et al. GCN 1470)\nwith the USNOFS 1.0-m telescope on one photometric night.  Stars\nbrighter than V=14.0 are saturated and should be used with care.\nWe have placed the photometric data on our anonymous ftp site:\nftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb020813.dat\nThe astrometry in this file is based on linear plate solutions\nwith respect to UCAC2.  The external errors are less than 100mas.\n\nWhile the night was photometric, the extinction was high\ndue to nearby forest fires.  The GRB field is towards\nour southern horizon and so there is a greater risk of\nzeropoint errors due to nonuniform smoke.  We estimate the\npresent zeropoint errors to be about 0.03mag.\nThe current calibration also has a brighter limiting magnitude\nthan normal due to the moonlit sky.  We will be extending this\ncalibration fainter and with additional nights to ensure against\na systematic zeropoint error.  You should check the dates on\nthe .dat file prior to final publication to get the latest photometry.",
  "circularId": 1503,
  "createdOn": 1029610031000,
  "email": "aah@nofs.navy.mil",
  "subject": "GRB020813, UBVRI field calibration",
  "submitter": "Arne A. Henden at USNO/USRA  <aah@nofs.navy.mil>",
  "eventId": "GRB 020813"
}