TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4041 SUBJECT: GRB050922C - Swift UVOT preliminary analysis DATE: 05/09/26 21:13:03 GMT FROM: Caryl Gronwall at PSU/Swift-UVOT S. D. Hunsberger (PSU), F. Marshall (GSFC), S. T. Holland (GSFC), P. Brown (PSU), A. Morgan (PSU), P. Roming (PSU), and A. Cucchiara (PSU) on behalf of the Swift/UVOT teams The UVOT began observing GRB050922C at 19:57:41UT, 111 seconds after the BAT trigger (Norris et al., GCN 4013). A fading optical counterpart is detected at 21:09:33.0 -08:45:30.1. The afterglow is apparent in the UBV filters and there is a marginal detection in UVW1 which is likely due to the redward edge of the filter response overlapping the U bandpass. The UVOT magnitudes listed below are not corrected for extinction. Tmid is the time since trigger of the midpoint of the exposure(s). Filter Tmid(s) Exp(s) Mag V 115.5 99.8 14.60 +- 0.10 V 374.5 9.8 15.49 +- 0.17 V 543.5 9.8 15.99 +- 0.21 V 712.5 9.8 16.01 +- 0.21 V 4543.5 899.8 17.62 +- 0.11 V 15962.5 899.8 18.89 +- 0.21 V 28443.5 899.8 19.95 is 3sigma upper limit B 261.5 9.8 15.88 +- 0.13 B 430.5 9.8 16.36 +- 0.15 B 598.5 9.8 16.45 +- 0.16 B 767.0 8.4 16.91 +- 0.20 B 11133.5 899.8 19.12 +- 0.11 B 22648.5 899.8 20.13 +- 0.21 B 39108.5 897.3 20.70 +- 0.38 B 50681.5 899.8 20.74 +- 0.39 U 246.5 9.8 15.09 +- 0.19 U 416.5 9.7 15.69 +- 0.20 U 584.5 9.8 15.84 +- 0.21 U 753.5 9.7 16.00 +- 0.21 U 10226.5 899.8 18.58 +- 0.18 U 21749.0 900.0 19.13 +- 0.20 U 34939.5 507.6 19.88 +- 0.31 U 46660.0 814.1 19.89 +- 0.26 UVW1 487.0 68.6 17.70 +- 0.29 (co-added 10s exposures) UVW1 6233.5 651.1 19.96 +- 0.41 UVW1 17730.0 806.0 20.18 is 3sigma upper limit UVM2 473.0 68.5 18.86 is 3sigma upper limit (co-added) UVM2 5450.5 899.8 20.48 is 3sigma upper limit UVW2 487.5 58.8 19.30 is 3sigma upper limit (co-added) UVW2 11969.5 753.2 20.62 is 3sigma upper limit Magnitudes are based on preliminary zeropoints, measured in orbit, and may require further refinement.