TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3717 SUBJECT: Swift/UVOT photometry of GRB050730 DATE: 05/07/31 20:48:41 GMT FROM: Alexander Blustin at MSSL-UCL A. J. Blustin (UCL-MSSL), S. T. Holland (GSFC/USRA), A. Cucchiara (PSU), N. White (GSFC), D. Hinshaw (GSFC-SPSYS) on behalf of the Swift/UVOT team report: Swift/UVOT began observing GRB050730 at 2005-07-30T20:00:22, 119 s after the BAT trigger (Holland et al. GCN 3704). A bright source was detected in the genie image at 14h 08m 17.09s,-3d 46' 18.9" (Holland et al. GCN 3704). Further analysis of data returned via the Malindi ground station shows that this source is fading; we report the following V band lightcurve, including detections significant at greater than 2.8 sigma: Tmid (s) Exp (s) Magnitude 170 99.77 17.842 +/- 0.152 300 9.78 17.473 +/- 0.380 384 9.78 17.477 +/- 0.383 468 9.78 16.737 +/- 0.238 553 9.76 16.568 +/- 0.216 637 9.76 17.119 +/- 0.302 722 9.78 16.706 +/- 0.231 3978 99.77 18.274 +/- 0.259 11948 837.11 19.200 +/- 0.150 23520 835.72 20.211 +/- 0.371 35088 843.21 20.286 3-sigma upper limit Where Tmid is the time after trigger of the mid-point of the exposure. Additionally the source was detected at greater than 2.8 sigma significance in the B-band in 3 images: Tmid (s) Exp (s) Magnitude 271 9.76 18.874 3-sigma upper limit 355 9.77 18.303 +/- 0.321 440 9.77 18.662 3-sigma upper limit 524 9.76 18.492 +/- 0.364 608 9.76 18.766 3-sigma upper limit 693 9.77 18.076 3-sigma upper limit 777 9.76 18.734 3-sigma upper limit 10164 899.77 20.447 +/- 0.208 21737 899.73 21.087 3-sigma upper limit 33309 901.43 21.126 3-sigma upper limit There was no detection in U or in any of the UV filter exposures. The upper limits for the summed images in these bands are: Filter T range (s) Exp (s) 3-sigma magnitude upper limit U 252-29724 2490.71 21.747 UVW1 238-28880 3665.12 21.98 UVM2 224-27972 3620.41 22.30 UVW2 281-34660 2765.25 22.40 where T range is the time range post-trigger over which the images were taken. The magnitudes are based on preliminary zero points, measured in orbit, and will require refinement with further calibration. All magnitudes are uncorrected for Galactic reddening.