TITLE: GCN CIRCULAR NUMBER: 12039 SUBJECT: GRB 110521A: Swift/UVOT Upper Limits DATE: 11/05/22 09:22:55 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 110521A 105 s after the BAT trigger (Oates et al., GCN Circ. 12031). No optical afterglow consistent with the XRT position (Beardmore et al., GCN Circ. 12034) 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) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag --------------------------------------------------------------- white_FC 105 255 147 >20.4 u_FC 263 513 246 >20.0 white 105 6615 766 >21.0 v 594 41254 2261 >20.5 b 519 30377 1766 >21.1 u 263 36155 3624 >21.7 w1 644 35466 3860 >22.0 m2 618 41934 3564 >22.3 w2 570 40340 2262 >22.3 -------------------------------------------------------------- The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.09 in the direction of the burst (Schlegel et al. 1998).