GCN Circular 476
S. Jha, R. Kirshner, K. Stanek, P. Garnavich, M. Garcia, A. Szentgyorgyi (CfA), and J. Tonry (U. Hawaii) report: We imaged the optical transient reported by Uglesich et al. (GCN 472) with the U. Hawaii 2.2-m telescope on Dec 17.61 UT. The source is clearly detected in each of two 300s R-band exposures. Though conditions were photometric, the observations were made at high airmass (~3), making precise absolute photometry difficult. Differential photometry with respect to 30 USNO-A2.0 stars in the images yields a magnitude estimate for the transient of R = 19.4 +/- 0.1 (internal error). This is the same magnitude derived by Uglesich et al. for their Dec. 17.312 UT observation, but it is possible that our two zeropoints are not identical. With respect to the reference star used by Henden et al. (GCN 473), we find an R magnitude difference of 4.29 magnitudes. This together with the data of Henden et al. gives an R-band power-law decay index of 1.0 +/- 0.2. Given the lack of a precise calibration for comparison stars in the field, we also list the R magnitude difference between the transient and two stars very near the transient from our Dec 17.61 UT images: Star Position (J2000) Transient - Star A (USNO-A2.0 975.01388002) 05:09:29.799 +11:17:08.47 +4.12 mag B (anonymous) 05:09:32.132 +11:17:23.75 -0.04 mag A finder chart with the proposed comparison stars labelled is available at http://cfa-www.harvard.edu/cfa/oir/Research/GRB/grb991216.jpg. This message can be cited.