TITLE: GCN CIRCULAR NUMBER: 27532 SUBJECT: GRB 200410A: Swift/UVOT Detection DATE: 20/04/10 21:38:49 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (UCL-MSSL) and K. K. Simpson (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 200410A 104 s after the BAT trigger (Simpson et al., GCN Circ. 27518). A source consistent with the XRT position (Goad et al. GCN Circ. 27522) is detected in the initial UVOT exposures. The uvot position has been determined from the first white image to be RA = 19:58:35.3 Dec = +51:46:53.0 or 299.64717 =51.78138 Deg (J2000) with an error estimate of 0.5". There are two nearby stars visible at 4 and 6 arcsec. 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 104 254 147 19.51 +/- 0.14 v 5051 6869 396 21.23 +/- 0.90 b 572 1519 98 19.61 +/- 0.32 u 317 567 246 20.39 +/- 0.37 w1 696 1294 57 >19.8 m2 671 1220 57 >20.0 w2 622 1270 57 >19.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.15 in the direction of the burst (Schlegel et al. 1998).