TITLE: GCN CIRCULAR NUMBER: 6573 SUBJECT: GRB 070621: Swift/UVOT Upper Limits DATE: 07/06/22 17:22:32 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland (CRESST/GSFC/USRA) and B. Sbarufatti (INAF-IASFPA) report on the behalf of the Swift UVOT team: The Swift/UVOT observed the field of GRB 070621 starting 120 s after the BAT trigger (Sbarufatti, et al. 2007, GCN Circ. 6560). We do not find any source, in any of the UVOT observations, inside the refined XRT error circle (Sbarufatti, et al., 2007 GCN Circ. 6567), or at the location of the NOT source (Malesani, et al. 2007, GCN Circ. 6565). The 3-sigma upper limits for detecting a source inside the refined XRT error circle in the initial data products are: Filter T_start T_stop Exp(s) Mag (3-sigma upper limit) ----------------------------------------------------------------- V 226 1360 806 20.2 B 702 714 10 18.6 U 680 4799 88 19.7 UVW1 656 4744 236 20.3 UVM2 631 802 38 18.8 UVW2 733 752 19 18.1 White 120 954 204 21.3 ----------------------------------------------------------------- The values quoted above are not corrected for the expected Galactic extinction corresponding to a reddening of E_{B-V} = 0.05 mag in the direction of the burst (Schlegel et al. 1998).