TITLE: GCN CIRCULAR NUMBER: 10394 SUBJECT: GRB 100206A: Swift/UVOT Upper Limits DATE: 10/02/07 17:03:04 GMT FROM: Frank Marshall at GSFC F.E. Marshall (NASA/GSFC) and H.A. Krimm (CRESST/GSFC/USRA) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 100206A 78 s after the BAT trigger (Krimm et al., GCN Circ. 10376). No optical afterglow consistent with the refined XRT position (Goad et al., GCN Circ. 10378) or the candidate optical afterglow position (Levan et al., GCN Circ. 10386) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC) exposures and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 78 228 147 >20.5 u_FC 290 540 246 >20.1 white 78 7046 647 >21.4 v 619 7457 553 >20.1 b 545 13655 1223 >21.2 u 290 12756 1464 >20.5 w1 668 7866 510 >20.7 The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.38 in the direction of the burst (Schlegel et al. 1998).