TITLE: GCN CIRCULAR NUMBER: 16109 SUBJECT: GRB 140413A: Swift/UVOT Observations of the Optical Afterglow DATE: 14/04/14 12:50:51 GMT FROM: Stephen Holland at STScI S. T. Holland (STScI) and V. D'Elia (ASDC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 140413A 2221 s after the BAT trigger (D'Elia et al., 2014, GCNC 16098). The preliminary UVOT position is RA (J2000) 04:21:49.23 = 65.45512 (deg) Dec (J2000) -51:10:58.0 = -51.18278 (deg) with an estimated uncertainty of 1.79 arcsec (radius, 90% confidence, statistical + systematic). We detect the optical afterglow at the position reported by Varela et al. (2014, GCNC 16099). Preliminary UVOT photometry and 3-sigma upper limits are presented below. ---------------------------------------------------------------- Filter TSTART TSTOP Exposure Mag Err Sigma ---------------------------------------------------------------- v 2377 4303 375 >19.7 b 2476 3747 235 >21.0 u 2451 3542 236 >19.9 uvw1 2427 3336 236 >19.8 uvm2 2931 3131 197 >19.5 uvw2 3957 4157 197 >20.1 white 2221 2370 147 >20.3 3752 3951 197 21.10 0.29 3.8 ---------------------------------------------------------------- The quoted magnitudes and upper limits have not been corrected for the Galactic extinction along the line of sight to this burst of E_{B-V} = 0.01 mag (Schlafly et al. 2011, ApJS, 737, 103). The photometry is in the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373).