TITLE: GCN GRB OBSERVATION REPORT NUMBER: 310 SUBJECT: GRB 990510 optical observations DATE: 99/05/10 20:35:55 GMT FROM: Titus Galama at U.Amsterdam P.M. Vreeswijk, T.J. Galama, E. Rol (U. of Amsterdam), K. Pollard (U. of Canterbury), J. Menzies (SAAO), P. Sackett (U. of Groningen), K. Sahu (STScI), J. van Paradijs (U. of Amsterdam and U. of Alabama in Huntsville), and C. Kouveliotou (USRA/MSFC) report on behalf of the PLANET microlensing team and the Amsterdam/Huntsville GRB optical follow-up team: "We have observed the error box of GRB 990510 (Dadina et al. 1999; IAU Circular 7160) with the Sutherland 1.0m telescope (South Africa) in B and R (several exposures of 1200 sec) on May 10.72 UT. Comparison of the images with the DSS (2nd Epoch Survey of the UK Schmidt; RG610 filter) reveals a bright object at RA 13:38:07.62, DEC -80:29:48.8 (J2000; estimated positional uncertainy of about 2"), which is not detected in the DSS. By comparison with a couple of USNO stars we estimate R = 19.2 +- 0.3. We strongly urge further observations to be made of this possible GRB counterpart." A finding chart can be found at http://www.astro.uva.nl/~titus/grb990510.html This message is citeable.