GCN Circular 462

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
Not found
 
 
 and #453
Not found
 
 
) 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
Not found
 
 
 and #456
Not found
 
 
) 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."


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