TITLE: GCN CIRCULAR NUMBER: 19530 SUBJECT: GRB 160611A: Swift/UVOT observations DATE: 16/06/12 18:52:25 GMT FROM: Massimiliano de Pasquale at IASF-Palermo M. De Pasquale (UCL-MSSL) and D. Malesani (DARK/NBI) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 160611A 2687 s after the BAT trigger (Malesani et al., GCN Circ. 19522). Very close to the XRT error circle (Osborne et al. GCN Circ. 19523), two sources are detected in the UVOT images. These sources are also detected in the Digitized Sky Survey (DSS) and are listed in the USNO catalog. Their light would blend with any new source at the XRT position, making the analysis more delicate. None of the two sources shows any significant flux decrease in the white filter between the first two white exposures (mid-time: 3071 s after the trigger) and the last three white exposures (mid-time: 10030 s after the trigger). Similarly, we find no significant decrease of the flux of the two sources in the u filter between the first u filter exposure (mid-time: 2946 s) and the last one (mid-time: 8560 s). We conclude that no optical afterglow consistent with the XRT position is detected in the UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: Filter T_start(s) T_stop(s) Exp(s) Mag white 2687 3456 344 >19.6 white 9578 10478 880 >19.8 v 3668 3867 197 >18.1 b 3051 9573 1082 >18.9 u 2846 8660 393 >19.6 w1 4078 5167 191 >19.7 m2 3873 4072 197 >19.4 w2 3463 10905 611 >20.6 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.22 in the direction of the burst (Schlegel et al. 1998).