GCN Circular 166
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.