TITLE: GCN CIRCULAR NUMBER: 22454 SUBJECT: GRB 180224A: Swift/UVOT Detection DATE: 18/02/26 17:54:14 GMT FROM: Sam LaPorte at PSU GRB 180224A: Swift/UVOT Detection S. J. LaPorte (PSU) and A. Y. Lien (GSFC/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180224A 85 s after the BAT trigger (Lien et al., GCN Circ. 22442). A fading source consistent with the XRT position (Evans et al. GCN Circ. 22443) also detected by (Lipunov et al. GCN Circ. 22444; Watson et al. GCN Circ. 22446; Pozanenko et al. GCN Circ. 22448) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 13:30:44.10 = 202.68377 (deg.) Dec (J2000) = +38:04:44.5 = 38.07902 (deg.) with an estimated uncertainty of 0.46 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 61 211 294 18.9 +/- 0.07 white 553 5337 287 20.7 +/- 0.33 v 603 1397 97 >18.4 b 552 1348 78 >19.5 u 273 5063 500 >20.3 w1 652 1446 97 >18.7 m2 824 844 19 >18.2 w2 751 771 19 >17.6 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.01 in the direction of the burst (Schlegel et al. 1998).