TITLE: GCN CIRCULAR NUMBER: 14738 SUBJECT: Swift/UVOT observations of GRB130603A DATE: 13/06/03 19:36:24 GMT FROM: Massimiliano de Pasquale at MSSL-UCL M. De Pasquale (MSSL/UCL) and A. Melandri (INAF/OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 130603A 3325 s after the BAT trigger (Melandri et al., GCN Circ. 14731). The uncatalogued source reported in Melandri et al., GCN Circ. 14732, is detected in the summed exposures. Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the summed exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 3686 5322 393 19.61 ± 0.15 v 4097 5562 197 >19.02 b 3481 16641 1278 19.71 ± 0.15 u 3275 15729 1278 19.19 ± 0.13 uvw1 4507 4707 197 19.62 ± 0.39 (2.8 sigma) uvm2 4302 4502 197 >19.63 uvw2 3892 5528 393 20.25 ± 0.37 (2.8 sigma) The possible detection of the optical source in uw2 filter indicates a redshift z < ~1.5 for this event. The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.06 in the direction of the burst (Schlegel et al. 1998).