TITLE: GCN GRB OBSERVATION REPORT NUMBER: 83 SUBJECT: GRB980519 Optical Observations DATE: 98/05/20 23:16:27 GMT FROM: Fredrick J Vrba at USNO GRB980519 Optical Observations The U. S. Naval Observatory GRB team (F. J. Vrba, B. Canzian, S. E. Levine, H. H. Guetter, A. A. Henden, C. B. Luginbuhl, J. A. Munn), D. H. Hartmann (Clemson Univ.), and M. C. Jennings (IGPP, UCR visitor) report follow up optical photometry of the variable object found by Jaunsen et al. (GCN Report 78) within the BeppoSAX error circle of GRB980519 (see GCN Report 75). Observations were obtained with the USNO Flagstaff Station 40-inch telescope between UT 1998 May 20.143 and 20.328 under the pole and again between UT 1998 May 20.426 and 20.464 when the field could be re-acquired at large hour angle. Four sets of observations were obtained in the Cousins R filter, two in the Cousins I filter, and one in the Johnson/Cousins V filter. Each set of observations consisted of three co-added and dithered images of 10 minutes each. The observations were obtained through variable cirrus clouds and haze. Preliminary reductions of the R-filter data by comparing with the magnitudes of stars A, B, and C as given in GCN Report 80 yield: UT Date R (mag) 1998 May 20.163 20.39 +/- 0.12 20.229 20.77 +/- 0.15 20.287 20.87 +/- 0.13 20.445 21.15 +/- 0.13 The uncertainties reflect both the internal photometry errors and the scatter in the magnitude offsets to stars A, B, and C. These data are consistent with the single R magnitudes from the MDM telescope (GCN Report 80) and the APO 3.5-m telescope (GCN Report 82). The lightcurve derived from these combined datapoints can be found on our web site at: http://psyche.usno.navy.mil/nofs/grb/grb980519.html. During this time interval the data do not appear to be consistent with a simple power law decrease in brightness. In a more detailed analysis we plan to also reduce these data with respect to two TYCHO stars within our CCD FOV and to analyze the V and I data to investigate colors. For further information contact F. J. Vrba at fjv@nofs.navy.mil or by telephone at (520) 779-5132. This GCN note can be cited.