TITLE: GCN CIRCULAR NUMBER: 6160 SUBJECT: GRB 070227: Swift/UVOT Upper Limits DATE: 07/02/28 23:52:35 GMT FROM: Shashi Pandey at MSSL S. B. Pandey (UCL-MSSL) and C. Pagani (PSU) report on behalf of the Swift/UVOT Team: The Swift/UVOT started observing the field of GRB 070227 (trigger 262347) 56680 s after the BAT trigger (Pagani et al., GCN Circ. 6156). UVOT observations started late because the BAT observation did not result in an automated response, but was found during the ground analysis. The 3-sigma upper limits for detecting a source inside the XRT error circle (Pagani, Grupe & Burrows, GCN Circ. 6157) in the co-added exposures are: Filter T_start T_stop Exp(s) Mag (3-sigma upper limit) --------------------------------------------------------------- V 56680 57586 885 20.90 B 63392 64113 702 21.58 U 62480 63386 885 21.31 UVW1 61573 62473 886 21.17 UVM2 57592 58329 726 21.34 UVW2 55773 56673 886 21.04 --------------------------------------------------------------- Caution should be taken due to the presence of a nearby bright star. The XRT error circle lies lies within the wings of the PSF of the bright star in all the UVOT frames. This complicates the photometry, so these limits could possibly be underestimated. The values quoted above are not corrected for the expected Galactic extinction E_{B-V} = 0.34 mag towards the direction of the burst (Schlegel et al. 1998).