TITLE: GCN CIRCULAR NUMBER: 21035 SUBJECT: GRB 170419A: Swift/UVOT Upper Limits DATE: 17/04/25 17:28:19 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 170419A 592 s after the BAT trigger (Sbarufatti et al., GCN Circ. 21013). No optical afterglow consistent with the XRT position (Goad et al. GCN Circ. 21015) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 592 742 147 >21.1 white 592 13376 1194 >22.0 v 748 19148 594 >19.6 b 846 7551 313 >20.4 u 822 23245 1108 >21.0 w1 797 7141 313 >20.0 m2 773 6935 274 >19.9 w2 1027 17141 672 >20.7 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.05 in the direction of the burst (Schlegel et al. 1998).