TITLE: GCN CIRCULAR NUMBER: 11482 SUBJECT: GRB 101219B: Swift/UVOT refined analysis DATE: 10/12/21 00:09:32 GMT FROM: Paul Kuin at MSSL N.P.M. Kuin (MSSL/UCL) and J.M. Gelbord (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 101219B 156 s after the BAT trigger (Gelbord et al., GCN Circ. 11473). The optical afterglow is at 7 arcsec distance of a 16th magnitude star. Special care has been taken to subtract the estimated contribution of the neghboring star. The data suggest that after an initial brightening, there was a dimming around T+550s followed by a second brightening. Preliminary magnitudes of the GRB, using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC) exposure and some selected subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag Mag_err white_FC 156 306 147.4 17.87 0.06 white 768 788 19.5 17.59 0.10 white 6686 6886 196.6 18.58 0.06 v 820 840 19.5 17.55 0.27 v 7097 7296 196.6 18.39 0.15 b 570 590 19.5 18.79 0.30 b 744 764 19.4 18.00 0.19 u 718 738 19.5 17.25 0.18 u 1298 1318 19.5 17.26 0.18 uvw1 1446 1465 19.4 17.43 0.28 uvw1 16352 16861 501 18.40 0.11 uvm2 7301 7392 89.6 18.15 0.24 uvm2 51175 52075 856 19.54 0.16 uvw2 6892 7092 197 18.04 0.13 uvw2 56901 57801 886 20.21 0.20 The values quoted above 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).