TITLE: GCN CIRCULAR NUMBER: 27602 SUBJECT: GRB 200416A: Swift/UVOT Detection DATE: 20/04/18 06:40:43 GMT FROM: Kira Simpson at PSU GRB 200416A: Swift/UVOT Detection K. K. Simpson (PSU) and P. A. Evans (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 200416A 102 s after the BAT trigger (Evans et al., GCN Circ. 27591). A source consistent with the XRT position (Evans GCN Circ. 27594) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 22:22:47.84 = 335.69934 (deg.) Dec (J2000) = -07:31:06.0 = -7.51833 (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 102 252 147 16.57 +/- 0.03 v 644 664 19 17.05 +/- 0.32 b 570 590 20 17.48 +/- 0.20 u 314 564 246 16.44 +/- 0.04 w1 694 714 20 16.59 +/- 0.23 m2 668 688 19 >16.3 w2 620 640 19 >17.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.06 in the direction of the burst (Schlegel et al. 1998).