TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3410 SUBJECT: GRB050509B: Optical observations at the Very Large Telescope DATE: 05/05/11 13:41:19 GMT FROM: Brian Lindgren Jensen at U.of Copenhagen GRB 050509B: Optical observations at the Very Large Telescope J. Hjorth, J. Sollerman, B. L. Jensen, J. P. U. Fynbo, P. Jakobsson, J. M. Castro Cerón, K. Pedersen, H. Pedersen, D. Watson (Niels Bohr Institute), R. Starling (Amsterdam), J. Gorosabel (IAA-CSIC Granada), E. Ramirez-Ruiz (IAS, Princeton), C. Kouveliotou (NASA/MSFC) on behalf of GRACE, report : "Using FORS2 on the 8.2m Antu Telescope at ESO/Paranal we have obtained 45 min R-band imaging (FWHM~0.7") of the XRT error circle for GRB 050509B (Swift trigger 118749, GCN 3381) at a mean epoch of May 11.0 UT. In the revised XRT error-circle (GCN 3395) we detect the four sources (S1-S4) mentioned in GCN 3401. None of these sources show pronounced variability with respect to the image posted in GCN 3401. The source previously designated S3 seems to be resolved into two sources separated by 1.8", or a new source is apparent in the centre of the error circle. The position of this source is: S5: RA(2000) = 12:36:13.88, Dec(2000) = +28:59:01.0 Another object is included just within the revised 90% XRT error-circle. The coordinates of this object is: S6: RA(2000) = 12:36.13.63, Dec(2000) = +28:59:07.7 An image of the field is shown at: http://www.astro.ku.dk/~brian_j/grb/grb050509B/ We plan to monitor the field with the VLT in the following weeks. We thank the Paranal Observatory staff, in particular Chris Lidman and Jura Borissova, for efficiently conducting the reported service-mode observations. " [GCN OPS NOTE(11may05): Per author's request, the RA value in source S6 was changed from "12:33.13.63" to "12:36.13.63".]