TITLE: GCN CIRCULAR NUMBER: 30991 SUBJECT: GRB 211025A: Swift/UVOT Detection DATE: 21/10/25 14:35:00 GMT FROM: Samantha Oates at MSSL <samantha.oates@alumni.ucl.ac.uk> S. R. Oates (U.Birmingham) and J. D. Gropp (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 211025A 131 s after the BAT trigger (Gropp et al., GCN Circ. 30986). A source consistent with the XRT position (Evans et al. GCN Circ. 30987) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 10:49:31.93 = 162.38304 (deg.) Dec (J2000) = +31:30:44.3 = 31.51231 (deg.) with an estimated uncertainty of 0.9 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 131 281 147 > 20.2 white 131 943 220 19.90 +/- 0.25 white 5965 6164 197 > 20.4 v 4940 6509 329 > 19.0 b 5760 5960 197 > 19.8 uvw1 669 688 19 > 17.5 uvw1 5350 5550 197 > 19.5 uvm2 5145 5345 197 > 19.4 uvw2 4735 6370 393 > 20.0 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.027 in the direction of the burst (Schlegel et al. 1998).