TITLE: GCN CIRCULAR NUMBER: 36968 SUBJECT: GRB 240727A: Swift/UVOT detection DATE: 24/07/28 20:09:28 GMT FROM: Paul Kuin at MSSL <npkuin@gmail.com> N. P. M. Kuin (UCL-MSSL) and T.M. Partosan (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 240727A 126 s after the BAT trigger (Partosan et al., GCN Circ. 36938). An optical afterglow consistent with the XRT position in GCN Circ 36956 (Gropp et al.) is detected in the initial UVOT exposures. The initial UVOT position found is RA=236.4375000 Dec=8.6202807 RA(J2000) = 15h 45m 45.0s Dec(J2000) = 08d 37' 12.9" with uncertainty = +/- 0.5" (90% confidence) 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 126 276 147 18.29 +/- 0.06 u_FC 285 535 246 17.92 +/- 0.08 b 541 561 20 >19.0 white 565 585 20 18.60 +/- 0.17 b 714 734 20 18.9 +/- 0.3 u 689 709 20 18.5 +/- 0.4 v 615 635 20 >18.0 w1 664 684 20 >17.8 m2 4622 4823 197 >18.7 w2 590 610 20 >17.7 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.037 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/36968. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...