TITLE: GCN GRB OBSERVATION REPORT NUMBER: 485 SUBJECT: GRB991216 Optical and infrared observations of Beethoven Burst DATE: 99/12/18 05:35:31 GMT FROM: Brad Schaefer at Yale U Bradley E. Schaefer (Yale) reports: "I have observed the afterglow of GRB991216 with the Yale 1m telescope on CTIO with B, R, and K filters last night and with B, V, R, I, and K filters tonight. The afterglow has faded by 1.15 +- 0.10 mag in the R-band between times 15.7 hours and 34.0 hours after the burst. This corresponds to a power-law decline of index -1.37 +- 0.12. The images show the optical transient to not be a point source, but to has some excess 'fuzziness' and extent. This could well be the underlying host galaxy. If so, then this might have one of the brightest hosts known, leading to possibilities of sharply defining the local environment of the progenitor in conjunction with the accurate radio position. A bright host would also suggest a relatively small red shift, perhaps appropriate for one of BATSE's brightest bursts. Last night, I obtained substantial UBVRIK images covering the preliminary RXTE error box. At the end of this time, the RXTE reported a revised error box that was just outside my FOV. By this time, the position was at airmass of 2.5, and I could only get one R-band, one B-band, and some K-band images. With the late arrival of the revised RXTE error box, it was up to observatories farther west to identify the afterglow by its variability. On the second night, I am in the middle of taking BVRIK images in two batches (to allow interpolation to a common time). Here is a listing of the YALO data for the first two nights which shows the afterglow source: 1999 Dec 17 07:47 UT R-band 10 minutes 1999 Dec 17 07:58 UT B-band 10 minutes 1999 Dec 17 07:47 UT K-band 19 x 1 minute 1999 Dec 18 01:58 UT K-band 30 x 1 minute 1999 Dec 18 01:58 UT I-band 5 minutes 1999 Dec 18 02:05 UT R-band 5 minutes 1999 Dec 18 02:12 UT V-band 10 minutes 1999 Dec 18 02:23 UT B-band 10 minutes 1999 Dec 18 ~06:00 UT K-band 30 x 1 minute 1999 Dec 18 ~06:00 UT I-band 5 minutes 1999 Dec 18 ~06:00 UT R-band 5 minutes 1999 Dec 18 ~06:00 UT V-band 10 minutes 1999 Dec 18 ~06:00 UT B-band 10 minutes Photometric standards were obtained also, but these data have not been reduced yet."