TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3393 SUBJECT: GRB 050509b: Optical observations DATE: 05/05/09 15:30:00 GMT FROM: Ken ichi Torii at RIKEN K. Torii (Osaka U.) reports: "The error region of the Swift short hard GRB 050509b (Hurkett et al. GCN 3381; Barthelmy et al. GCN 3385) was imaged with the 0.3 m telescope in the New Mexico Skies observatory. The observation started at 2005 May 9, 04:08:52 UT (513 s after the trigger) and 120 s integrations in I and V bands were obtained. The optical counterpart candidate (Bloom et al. GCN 3388; Cenko et al. GCN 3391) of the XRT source (Kennea et al. GCN 3383) is not detected in our frames while the candidate host galaxy is detected. The plate scale of our images is 1".41/pixel and the optical counterpart candidate should be readily resolved from the galaxy. We therefore derive the following 3 sigma upper limits for the optical counterpart candidate (GCN 3388; GCN 3391) relative to USNO-B1.0 I magnitude. MidTime(UT) Filter Exposure Mag --------------------------------- 04:09:52 I 1x120s >18.7 04:15:59 I 3x120s >19.2 --------------------------------- "