[vsnet-grb-info 2039] GRB050824: Swift/UVOT detection of fading afterglow

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3878
SUBJECT: GRB050824: Swift/UVOT detection of fading afterglow
DATE:    05/08/25 17:41:46 GMT
FROM:    Patricia Schady at MSSL/Swift  <ps at mssl.ucl.ac.uk>

The Swift Ultra-Violet/Optical Telescope (UVOT) observations began at
00:53:49 UT, 1.8 hrs after the BAT trigger. UVOT detects a fading source at a 
position consistent with that reported by Gorosabel et al. (GCN 3865) in 5 
of its 6 filters. The magnitudes or 3-sigma upper limit in the first 
exposure taken in each filter are as follows:

Filter  Mid Time (hrs)  Exp (s)  Mag/3-sig UL
V	1.8		109	20.02+/-0.39
B	5.1		305	20.88+/-0.36
U	3.6		217	19.55+/-0.32
W1	9.5		205	19.85+/-0.33
M2	11.7		121	19.34+/-0.36
W2	12.3		1457	> 20.79	

The afterglow has faded below 2-sigma above background 11hrs after the 
burst trigger in all filters apart from the V and U, where it is still 
detected at the 2.3-sigma and >3-sigma level, respectively.

The magnitudes have not been corrected for extinction. These magnitudes 
are based on preliminary zero-points, measured in orbit, and will require 
refinement with further calibration.