TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3123 SUBJECT: GRB 050318: SWIFT-UVOT refined analysis DATE: 05/03/19 22:42:15 GMT FROM: Martin Still at NASA/GSFC Swift SSC M. De Pasquale (MSSL), P. Boyd (GSFC/UMBC), S. T. Holland, M. Still (GSFC/USRA), W. Landsman (GSFC), S. Hunsberger (PSU), A. Breeveld (MSSL), P. Roming (PSU), K. Mason, P. Schady (MSSL), M. Ivanushkina (PSU), T. Poole (MSSL), C. Gronwall (PSU), A. Blustin (MSSL), P. Brown (PSU), S. Rosen, K. McGowan (MSSL), S. Koch (PSU), M. Carter, H. Huckle (MSSL), P. Broos (PSU), T. Kennedy, P. Smith, B. Hancock (MSSL), H. Krimm (GSFC/USRA), J. Nousek (PSU), N. Gehrels (GSFC), on behalf of the Swift UVOT team. Analysis of a more complete data set from the Swift-UVOT of GRB 050318 (Krimm, et al., GCN 3111) yields an improved position from stacked V image exposures of RA = 03h 18m 51.15(2)s, Dec = -46d 23m 43.7(3)s (J2000). Images in various filters, stacked over the first 34 ksec after the trigger indicate time-averaged instrumental magnitudes of UVW2 > 22.0, UVM2 > 22.1, UVW1 > 21.5, U = 20.5(2), B = 20.0(1) and V = 19.7(1). This indicates either a highly reddened source, or an object of redshift z ~ 2.7 in front of the burst. Magnitudes are based on ground calibration and will require confirmation in flight.