TITLE: GCN CIRCULAR NUMBER: 24587 SUBJECT: GRB 190511A: Swift/UVOT further analysis DATE: 19/05/17 20:15:07 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (UCL-MSSL) and M. G. Bernardini (INAF-OAB) report on behalf of the Swift/UVOT team: In GCN Circ. 24494 (Kuin and Bernardini) we described how we detect the afterglow of the GRB, but that the photometry was affected by an object located at a distance of 1.3 arcsec. Further Swift observations show that the uv-optical afterglow was no longer detected in white beyond 26ks after the trigger. Data that were taken after that time are considered template observations that provide the background contribution to the photometry. The template net corrected count rates, with instrumental effects removed, are found to be as follows for a 3" radius circular aperture at the location of the GRB as reported in GCN 24494: White = 1.066 +/- 0.031 c/s; u = 0.149 +/- 0.016 c/s; b = 0.509 +/- 0.061 c/s; uvw2 = 0.011 +/- 0.011 c/s; v = 0.272 +/- 0.042 c/s; while uvm2 and uvw1 were not observed until after the afterglow became too faint. After removal of the template contribution, the following preliminary detections and 3-sigma upper limits were determined from the count rates using the zeropoints in the UVOT photometric system (Poole et al. 2008, MNRAS 383, 627; Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the image mode exposures: Filter T_start(s) T_stop(s) Exp(s) Mag white 131 281 147 15.96 +/- 0.05 u 290 385 93 19.62 +/- 0.42 b 5684 5884 197 > 20.13 white 5888 6088 197 20.61 +/- 0.37 uvw2 6094 11850 518 > 17.81 v 17150 17450 300 > 19.35 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.09 in the direction of the burst (Schlegel et al. 1998).