TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3549 SUBJECT: CORRECTION: GRB050603 Swift UVOT Afterglow Observations DATE: 05/06/15 01:37:36 GMT FROM: Peter Brown at PSU P. Brown (PSU), A. Retter (PSU), P. Schady (MSSL), P. Boyd (GSFC), S. T. Holland (GSFC/USRA), P. Roming (PSU), C. Gronwall (PSU), N. Cucchiara (PSU), K. Mason (MSSL), N. Gehrels (GSFC), on behalf of the Swift UVOT team: The second V-filter magnitude (V=21.8 at T_start=32997) reported in GCN 3516 for the fading afterglow of GRB050603 is incorrect. An error in the on-board shift-and-add code resulted in an unusually large amount of missing data for this exposure that was not correctly recorded in the exposure information. The real exposure time for the second exposure was adjusted to 101 s to match the actual data contained in the image. The corrected magnitude is 18.7, meaning the afterglow only faded by 0.5 magnitudes between the two observations reported in GCN 3516. In addition, we report the afterglow magnitude in later exposures. An error-weighted powerlaw fit gives a decay index of 1.97 +/- 0.22. The corrected and new afterglow magnitudes from UVOT are as follows: Time (h) Mag Filter Duration (s) 9.5 18.2 +/- 0.1 V 1298 10.9 18.7 +/- 0.4 V 101 12.7 19.5 +/- 0.2 V 1772 14.4 19.3 +/- 0.2 V 2104 15.9 19.0 +/- 0.2 V 1200 17.8 19.7 +/- 0.3 V 1205 20.8 20.1 +/- 0.4 V 1948 36.1 21.1 +/- 0.4 V 10,458 (9 exposures coadded) Time (h) is the midpoint of the exposure given in hours after the burst trigger. The reported errors do not include a +/- 0.09 error in the preliminary inflight zero point calibration.