TITLE: GCN CIRCULAR NUMBER: 21415 SUBJECT: GRB 170804A: Swift/UVOT Detection DATE: 17/08/04 21:03:59 GMT FROM: Samantha Oates at MSSL S. R. Oates (U. Warwick) and A. Cholden-Brown (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 170804A 132 s after the BAT trigger (Cholden-Brown et al., GCN Circ. 21410). A fading source consistent with the XRT position (Evans et al., GCN Circ. 21413) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 0:25:34.29 = 6.39288 (deg.) Dec (J2000) = -64:47:03.1 = -64.78419 (deg.) with an estimated uncertainty of 0.5 arc sec. (radius, 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 132 281 147 18.9 +/- 0.1 white 871 1020 147 20.0 +/- 0.2 u_FC 289 539 246 18.7 +/- 0.1 v 796 1243 58 >18.7 b 545 565 19 18.9 +/- 0.4 uvw1 671 1292 78 >19.0 uvw2 596 1392 97 >19.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998). --------------------------------------------- Dr Samantha Oates Leverhulme Early Career Fellow Department of Physics University of Warwick Coventry CV4, UK Tel: +44 (024) 765 23383 Email: s.oates@warwick.ac.uk -----------------------------------------------