TITLE: GCN GRB OBSERVATION REPORT NUMBER: 462 SUBJECT: R-band Observations of GRB991208 at TNG DATE: 99/12/16 15:46:06 GMT FROM: Nicola Masetti at ITeSRE,CNR,Bologna N. Masetti, E. Palazzi, E. Pian, F. Frontera (ITESRE, CNR, Bologna), S. Benetti, A. Magazzu' (TNG), A.J. Castro-Tirado (LAEFF-INTA and IAA-CSIC) and B.L. Jensen (Univ. of Copenhagen), on behalf of a larger collaboration, report: "R images of the optical afterglow of GRB991208 (GCN #452 and #453) were obtained between Dec. 12.29 and Dec. 15.29 UT at Roque de Los Muchachos (Canary Islands, Spain) with the 3.58-meter Telescopio Nazionale Galileo (TNG) + OIG CCD camera. We clearly detected the optical transient in all R images. The following table shows the results of these observations: Date (UT) Exptime Magnitude Seeing 1999 Dec 12.29 500 sec 20.25 +- 0.15 1".8 1999 Dec 13.29 360 sec 20.3 +- 0.2 1".6 1999 Dec 14.29 600 sec 21.25 +- 0.15 1".5 1999 Dec 15.29 900 sec 21.6 +- 0.3 1".5 (clouds) Photometric calibration was tied to the USNO A2.0 star 1350-08916561 (R = 15.85 +- 0.1 was assumed). Preliminary analysis of R data shows that these are consistent with a power-law decay with index alpha = -2.15 (GCN #454 and #456) with the exception of the observation of Dec. 13.29, which may however be affected by uncertainties associated with the observing conditions and with the shorter exposure time." This message can be cited.