GRB 991216 Optical Observations 

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  498
SUBJECT: GRB 991216 Optical Observations
DATE:    99/12/19 12:15:14 GMT

B. L. Jensen, H. Pedersen, J. Hjorth, J. Pritchard (U. of Copenhagen),

T. Abbott (NOT), A. J. Castro-Tirado (LAEFF-INTA, Madrid), E. Pian
(ITESRE, Bologna), P. Vreeswijk (U. of Amsterdam) and
J. Greiner (AIP, Potsdam) report on behalf of a larger European collaboration:

"We have obtained R-band exposures of the optical counterpart (GCN #472) using the Danish 1.5m at La Silla (Dec. 18) and the 2.5m Nordic Optical Telescope on La Palma (Dec. 19). When measured relative to star "A" (GCN #476, #486) we obtain the following magnitudes: 

Date (UT)      R                Exp    FWHM
  
 Dec. 18.112 :  20.12 +-0.1     3x300s  1.8"
 Dec. 18.324 :  20.40 +-0.1     3x300s  1.9"
 Dec. 19.10  :  20.90 +-0.1     4x300s  1.8"

When analyzed jointly with observations available from GCNs (excluding the Rc~21.1 from GCN #487) we deduce a power-law decay index of -1.17+-0.1. The corresponding plot is available at: http://www.astro.ku.dk/~brian_j/grb/grb991216/ ."