TITLE:   GCN CIRCULAR
NUMBER:  10973
SUBJECT: GRB 100724A:  Swift/UVOT observations
DATE:    10/07/24 15:21:51 GMT
FROM:    Craig Swenson at PSU/Swift  <cswenson@astro.psu.edu>

C. A. Swenson (PSU) and C. B. Markwardt (CRESST/GSFC/UMD) report
on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 100724A 
74s after the BAT trigger (Markwardt et al., GCN 10968).  We detect a 
source at the position of the detected X-ray source (Markwardt et al., 
GCN 10968) and the location reported by GROND (Olivares et al., GCN 
10969).  The source is clearly fading in the UVOT white filter between 
the first finding chart and a later observation.

The magnitudes and 3-sigma upper limits using the UVOT photometric 
system (Poole et al., 2008, MNRAS, 383, 627) for finding chart exposures 
(FC) and the summed images are:

Filter      T_start    T_stop    Exp(s)    Magnitude/3-sigma upper limit
----------------------------------------------------------------------
white (FC)      92       242      147            18.46 ± 0.11
white          584       775       39            > 19.71
u     (FC)     304       554      246            18.54 ± 0.15
u              706       726       19            18.17 ± 0.37
v               74      1050       60            > 18.31
b              559       751       39            > 18.99
uvw1           682       702       19            > 17.96
uvm2           658       850       39            > 18.19
uvw2           609      1034       58            > 18.97

The quoted upper limits have not been corrected for the expected 
Galactic extinction along the line of sight of E_(B-V) = 0.043 mag 
(Schlegel, et al., 1998, ApJS, 500, 525).