TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  305
SUBJECT: GRB 990506, optical observations
DATE:    99/05/10 17:55:55 GMT
FROM:    Arne A. Henden at USNO/USRA  <aah@nofs.navy.mil>

The U.S. Naval Observatory GRB team (F.J. Vrba, A.A. Henden, B.
Canzian, C.B. Luginbuhl, S.E. Levine, H.H. Guetter, J.A. Munn), D.H.
Hartmann (Clemson Univ.), M.C. Jennings (IGPP, UCR visitor)

report an updated BVRcIc photometry file for the field of GRB 990506.
This file can be found at:
  ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb990506.dat
Two photometric nights with a wide variety of
Landolt standards having large color and airmass differences were used.
We were more concerned with deep R-band imaging, and so only
calibrated the field with shorter BVRcIc exposures.  Typical errors are
0.05mag at V=18, with stars reported down to approximately V=20.
Star pairs that are separated by less than 5 arcsec are reported
as single objects or at least have their photometry contaminated
by their neighbors and should therefore be ignored.

This GCN note can be cited.