TITLE: GCN CIRCULAR NUMBER: 22605 SUBJECT: GRB 180404A: Swift/UVOT Detection DATE: 18/04/05 17:04:53 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) and J. D. Gropp (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180404A 90 s after the BAT trigger (Gropp et al., GCN Circ. 22589). A source consistent with the XRT position (Osborne et al. GCN Circ. 22592) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 05:34:11.64 = 83.54850 (deg.) Dec (J2000) = -37:10:03.9 = -37.16774 (deg.) with an estimated uncertainty of 0.50 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 (fc) 90 240 147 19.47 +/- 0.09 white 90 770 180 19.34 +/ -0.10 white 45830 52026 1028 >21.66 v 632 5179 99 >18.9 b 558 750 39 >19.4 u (fc) 302 552 246 18.95 +/- 0.12 u 303 726 265 18.95 +/ -0.14 w1 682 701 19 >17.8 m2 656 676 19 >17.4 w2 607 5094 216 19.45 +/- 0.28 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).