TITLE: GCN CIRCULAR NUMBER: 18075 SUBJECT: GRB 150724B: Swift/UVOT Detection DATE: 15/07/27 17:25:04 GMT FROM: Paul Kuin at MSSL N.P.M. Kuin(MSSL/UCL) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150724B 88.6ks after the LAT trigger (Bissaldi et al., GCN Circ. 18065), which was also observed at high energy by Fermi-GBM (Veres et al., GCN Circ 18066) and Konus-Wind (Golenetskii et al. GCN Circ. 18074). Five UVOT exposures were obtained of which the first two show a weak detection at the XRT position (Osborne et al., GCN Circ. 18069). Preliminary magnitudes and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: Filter T_start(s) T_stop(s) Exp(s) Mag white 88619 88799 178 19.64+-0.12 white 88802 90608 1765 20.99+-0.14 white 90614 90748 60 >19.53 white 94379 94558 176 >20.82 white 94562 96236 1648 >22.01 The brightness is consistent with the RATIR observation at 147ks in r and i (Butler et al, GCN 18072). The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.06 in the direction of the burst (Schlegel et al. 1998).