TITLE: GCN CIRCULAR NUMBER: 15476 SUBJECT: GRB 131108A: Swift/UVOT Detection DATE: 13/11/09 16:54:16 GMT FROM: Margaret Chester at PSU M.M. Chester and M. C. Stroh (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of the Fermi/LAT-detected GRB 131108A 25920 s after the LAT trigger (Racusin et al., GCN Circ. 15464). A source consistent with the XRT position (Stroh and Kennea GCN Circ. 15474) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 10:26:00.45 = 156.50187 (deg.) Dec (J2000) = +09:39:44.1 = 9.66225 (deg.) with an estimated uncertainty of 0.58 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 27746 28046 295 19.70 +/- 0.10 b 26833 27133 295 19.67 +/- 0.16 u 25920 26220 295 19.10 +/- 0.14 w1 31699 32599 886 20.96 +/- 0.33 m2 37465 37914 442 >20.6 w2 45446 49794 1069 >21.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.028 in the direction of the burst (Schlegel et al. 1998).