GCN Circular 485

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."