TITLE: GCN GRB OBSERVATION REPORT NUMBER: 351 SUBJECT: Optical Observations of GRB 990506 DATE: 99/06/15 18:34:56 GMT FROM: Josh Bloom at CIT Optical Observations of GRB 990506 J. S. Bloom, S. G. Djorgovski, S. R. Kulkarni, and B. A. Jacoby (Caltech), on behalf of the Caltech-NRAO-CARA GRB collaboration, report: "On June 11.25 UT, we obtained a total of 1500-s R-band integration of the field of GRB 990506 (Hurley et al.; GCN #290) with the Low-Resolution Imaging Spectrometer (LRIS) on the Keck II 10-m telescope on Mauna Kea, Hawaii. An astrometric plate solution was obtained relative to the USNO A2.0 catalog with a statistical error of 0.23, 0.26 arcsec (ra, dec). Coincident with the position of the fading radio source (Taylor et al.; GCN #350) is a faint extended (NE-SW) galaxy with an irregular (and possibly interacting) morphology. Assuming the star at ra: 11:54:54.7, dec: -26:41:15.2 (J2000) has R=18.5 (Henden et al; GCN #305), we find a preliminary magnitude of the presumed host galaxy of GRB 990506 to be R=24.8 +/- 0.2. This message can be cited."