TITLE: GCN CIRCULAR NUMBER: 10689 SUBJECT: GRB100425A: Swift/UVOT Upper Limits DATE: 10/04/25 18:00:55 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) and D. Grupe (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 100425A 88s after the BAT trigger (Grupe et al., GCN 10673). We do not detect a new source at the enhanced Swift XRT position (Goad et al. GCN 10686) and at the location of source B detected by the VLT telescope (Malesani et al. GCN 10680) and GROND telescope (Olivares et al. GCN 10683). Photometry is complicated by the prescence of the VLT source A within the source aperture. The 3-sigma upper limits for the finding chart exposures (FC) and summed images are: Filter T_start T_stop Exp(s) Mag (3-sigma upper limit) ------------------------------------------------------------- white (FC) 88 238 147 >19.37 white 88 5778 513 >19.59 u (FC) 301 551 246 >18.92 u 301 6796 650 >19.08 v 631 11961 1317 >19.76 b 556 5573 236 >19.71 uvw1 680 6600 432 >19.44 uvm2 4757 12580 997 >20.87 uvw2 606 11048 1318 >21.26 ------------------------------------------------------------- The quoted upper limits have not been corrected for the expected Galactic extinction along the line of sight of E_(B-V) = 0.15 mag. All photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383, 627).