TITLE: GCN CIRCULAR NUMBER: 9048 SUBJECT: GRB 090328: Swift UVOT observations DATE: 09/03/29 15:11:20 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) reports on behalf of the Swift/UVOT team: The Swift/UVOT began observing the field of GRB 090328 16 hrs after the Fermi LAT trigger (McEnery et al., GCN 9044). We detect a candidate optical afterglow in the u and white filters at: RA(J2000.0) = 06:02:39.67 DEC(J2000.0) = -41:52:54.5 with an estimated uncertainty of 0.6 arcsec (radius, 90% confidence). At the moment we are unable to tell if the source is fading, further observations have been performed, but due to a data gap, the data is currently unavaliable. Preliminary magnitudes for the white and u filters are: Filter T_mid (hrs) Exposure(s) Mag Err ------------------------------------------------------------ u 16.0 793 19.04 +/- 0.13 white 16.1 173 19.56 +/- 0.14 The above magnitudes are not corrected for the Galactic extinction corresponding to a reddening of E_{B-V} = 0.06 mag (Schlegel et al., 1998, ApJS, 500, 525). The photometry is on the UVOT flight system described in Poole et al. (2008, MNRAS, 383,627).