TITLE: GCN CIRCULAR NUMBER: 6336 SUBJECT: GRB070420: Swift UVOT continuing observations DATE: 07/04/20 16:57:52 GMT FROM: Stefan Immler at NASA/GSFC S. Immler (USRA/GSFC), F. E. Marshall (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC), and M. Stamatikos (NASA/ORAU) report on behalf of the Swift/UVOT team: The UVOT position sent out as a GCN notice gave an invalid position while GCN 6330 had the correct position. We regret any confusion this might have caused. The revised UVOT position of the afterglow is RA(J2000) = 08h04m55.17s, Dec(J2000) = -45d33'20.0". We estimate a statistical accuracy of 0.2 arcsec radius (90% confidence) but with a systematic uncertainty of the aspect solution of about 0.5 arcsec. The Swift/UVOT began taking data in the field of GRB070420 90s after the BAT trigger (Stamatikos et al., GCN 6330). The afterglow is detected in all UVOT optical filters. The large reddening, E(B-V) = 0.52, might explain the non-detection in the UV. The flux is decaying with t**-0.7 in the White for times between T+500 and T+10000 seconds. The photometry results are given for the 7 UVOT filters below. V T+(s) Exp(s) Mag White 109 99 17.4+/-0.1 7125 197 20.8+/-0.1 V 90 10 17.9+/-0.1 B 693 10 18.8+/-0.1 U 669 20 21.1+/-0.1 UVW1 645 20 >20.4 (3-sigma) UWM2 620 20 >20.8 (3-sigma) UVW2 723 20 >20.8 (3-sigma)