TITLE: GCN CIRCULAR NUMBER: 22565 SUBJECT: GRB 180329B: Swift/UVOT Detection DATE: 18/03/30 11:38:14 GMT FROM: Sam Emery at MSSL-UCL S.W.K. Emery (UCL-MSSL) and J. L. Racusin (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180329B 113 s after the BAT trigger (Racusin et al., GCN Circ. 22558). A fading source consistent with the XRT position (Beardmore et al. GCN Circ. 22559) also detected by the NOT (Perley et al. GCN Circ. 22562) and RATIR (Watson et al. GCN Circ. 22564) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 05:31:36.91 = 82.90381 (deg.) Dec (J2000) = -23:41:25.8 = -23.69051 (deg.) with an estimated uncertainty of 0.43 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 113 263 147 17.69 +/- 0.04 white 550 6892 599 17.64 +/- 0.03 v 601 5867 274 17.25 +/- 0.07 b 526 6687 452 17.94 +/- 0.05 u 271 6482 697 17.00 +/- 0.04 u 16039 39219 1961 18.74 +/- 0.07 w1 650 6277 452 18.72 +/- 0.14 m2 626 6073 274 >19.8 w2 577 7017 390 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998).