TITLE: GCN CIRCULAR NUMBER: 12157 SUBJECT: GRB 110709B: Swift/UVOT Observations DATE: 11/07/15 12:00:00 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland (CRESST/USRA/GSFC) and J. R. Cummings (CRESST/UMBC/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT observed the field of GRB 110709B starting 70 s after the BAT trigger (Cummings et al., 2011, GCNC 12122). Settled observations started at 91 s. We do not detect a source at the UVOT-enhanced XRT position (Beardmore, et al., 2011, GCNC 12136) in any of the UVOT filters. Preliminary 3-sigma upper limits for detecting a source in the finding charts and in the co-added images, are Filter TSTART TSTOP EXPOSURE Mag --------------------------------------------------- white (FC) & 91 & 241 & 147 & >21.1 u (FC) & 303 & 553 & 246 & >20.5 white (FC) & 858 & 1008 & 147 & >21.3 --------------------------------------------------- v & 633 & 64,817 & 3519 & >21.5 b & 558 & 54,124 & 3664 & >22.4 u & 303 & 59,906 & 4680 & >22.2 uvw1 & 682 & 59,264 & 4730 & >22.2 uvm2 & 1235 & 58,357 & 3732 & >22.3 uvw2 & 782 & 64,122 & 3530 & >22.4 white & 91 & 30,997 & 3107 & >23.0 --------------------------------------------------- We find weak evidence for variability at the location of the USNO-B1.0 source 3.5 arcsec WNW of the XRT position at the time of the second BAT trigger (Barthelmy et al. 2011, GCNC 12124). Preliminary photometry is Filter TSTART TSTOP EXPOSURE Mag Err Sigma ---------------------------------------------------------------- white & 91 & 241 & 147 & >21.1 3-sigma UL white & 583 & 776 & 39 & 20.08 0.35 3.3 white & 858 & 1008 & 147 & >21.3 3-sigma UL white & 1161 & 2047 & 117 & 20.96 0.36 3.1 white & 6245 & 6444 & 197 & >21.4 3-sigma UL white & 7679 & 11,397 & 340 & 21.07 0.37 3.1 white & 11401 & 12,005 & 590 & >21.9 3-sigma UL white & 17893 & 18,800 & 885 & 20.98 0.16 7.8 white & 30335 & 30,997 & 644 & 21.39 0.23 5.2 ---------------------------------------------------------------- We note that both the USNO-B1.0 source and the XRT position are located in the coincidence loss halo of a bright star, which makes precision photometry difficult. It is not clear if the apparent variability seen at the location of the USNO-B1.0 source is real or not. The quoted magnitudes and upper limits have not been corrected for the large, but uncertain, Galactic extinction along the line of sight to this burst (E_{B-V} = 0.05 mag, Schlegel et al. 1998, ApJS, 500, 525).