TITLE: GCN CIRCULAR NUMBER: 6177 SUBJECT: GRB 070306 Swift/UVOT refined analysis DATE: 07/03/07 13:34:33 GMT FROM: Massimiliano de Pasquale at MSSL-UCL M. De Pasquale, S.B. Pandey (MSSL/UCL) report on the behalf of the Swift UVOT team: Swift/UVOT observed the field of GRB070306 (Pandey et al. 2007, GCN 6169) starting 146s after the trigger with the settling expsoure. UVOT did not find any source inside the refined XRT error circle (Page et al. 2007, GCN 6172), down to the following 3 sigma upper limits in the White filter finding exposure and in the coadded frames in all filters: Filter t_start(s) t_stop(s) Exp(s) Mag 3-sig UL Wh_find 162 262 98 19.8 V 267 11158 1259 20.5 B 745 6257 403 21.5 U 721 6053 413 21.0 W1 697 5848 236 19.0 M2 673 5633 236 18.7 W2 773 6651 397 19.5 Wh 162 6462 512 20.7 These upper limits are not corrected for the small Galactic extinction, corresponding to a reddening of E(B-V)=0.03 (Schlegel et al. 1998), towards the direction of this burst.