TITLE: GCN CIRCULAR NUMBER: 9783 SUBJECT: GRB 090813: P60 Optical Afterglow Confirmation DATE: 09/08/13 05:25:55 GMT FROM: S. Bradley Cenko at Caltech S. B. Cenko (Caltech) reports on behalf of a larger collaboration: We have imaged the field of GRB090813 (Cummings et al., GCN 9781) with the automated Palomar 60 inch telescope. Observations were taken in the Sloan r', i', and z' filters beginning at approximately 4:12 UT (~ 2 minutes after the burst). Inside the XRT error circle we find a fading point source with coordinates (J2000.0): RA: 15:03:08.48 Dec: +88:34:05.5 with an estimated error of ~ 0.3" in each coordinate. Presumably this is the same source identified by Gorosabel et al. (GCN 9782). With reference to several USNO-B1 sources in the field, we measure the following I-band magnitudes for the afterglow: UT (mid-point) Exposure (s) Magnitude ---------------------------------------------------------------- 04:15:47 60 17.8 04:20:33 60 18.2 Further observations are planned.