TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3083 SUBJECT: GRB050309: Early optical limit from P60 DATE: 05/03/10 06:49:44 GMT FROM: Derek Fox at CIT Derek B. Fox and S. Bradley Cenko report on behalf of the Caltech-NRAO-Carnegie GRB collaboration: "Examination of a coadded R-band image from our P60 observations for the BAT localization region of GRB050309 (Barthelmy et al, GCN 3082), taken at a mean epoch of 10:55 UT (12 minutes after the burst), confirms our earlier report (Cenko & Fox, GCN 3080) of the absence of new optical sources to the limit of the Digitized Sky Survey and our own observations. We estimate this limit to be R < 20.5 mag as calibrated against the USNO B-1.0 catalog magnitudes of bright stars in the region. This limit applies to XRT source #2 (GCN 3082), where no emission is seen. The position of XRT source #1 is 6-arcsec (twice the FWHM in our images) from a bright star and USNO B-1.0 catalog object having R=12.98 mag. No extension of the catalog star is apparent in our images."