TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  166
SUBJECT: GRB981220 I-band Observations
DATE:    98/12/24 10:57:03 GMT
FROM:    Christian B. Luginbuhl at USNO/Flagstaff  <cluginbuhl@nofs.navy.mil>

GRB 981220 I-Band Observations 

The U. S. Naval Observatory GRB team (C. B. Luginbuhl, F. J. Vrba, A.
A. Henden, S. E. Levine, J. Munn, B. Canzian, H. H. Guetter), D. H.
Hartmann (Clemson Univ.), and M. C. Jennings (IGPP, UCR visitor) report
follwup I-band observations of the GRB 981220 localization reported in
GCN 164.  A second set of 6 dithered 10-min I-band exposures was
obtained with the USNO 1.55-m telescope and Tek 2K CCD on UT 1998
December 24 between UT 05:45:47 and UT 07:00:12.  The combined, median
filtered, and high-pixel rejected image can be viewed at the USNO
public website:  http://www.nofs.navy.mil/news/grb/grb981220.html
beginning sometime 24 December.  The seeing was again rather poor
(1.7-1.9 arcsec, FWHM).

No obvious fading or brightening sources are detected to a preliminary
estimated limiting magnitude of I=22.  The source marked "1" on the ARC
3.5m image taken by Dierks and Deutsch
(http://www.astro.washington.edu/deutsch/grb/grb981220/) seems
approximately constant in this preliminary analysis.  Complete
photometric reduction of the two nights' USNO observations to determine
the variance vs. magnitude relation and look for outliers is underway,
and will be reported in a followup GCN later today.

This GCN Note can be cited.