GCN Circular 9954

N.P.M. Kuin (MSSL-UCL) and D. Grupe (PSU) report on behalf
of the Swift/UVOT team:

The Swift/UVOT began a delayed observing the field of GRB 090927
2121s after the trigger due to an observing constraint (Grupe, GCN
Circ. 9945
Not found
 
 
). We detect a fading optical afterglow in white, v,b,
and u filters at the position reported by UVOT (Gronwall et al.,
GCN Circ. 9946
Not found
 
 
).

Preliminary magnitudes are reported below.

Filter   T_start(s) T_stop(s) Exposure(s) Magnitude
===================================================
white(FC)    2141    2291    147.4    19.13 +/- 0.09
white        2372    2920    235.6    19.40 +/- 0.09
v            2121    2617     48.6    19.0  +/- 0.37
v            3131    3331    196.6    19.37 +/- 0.25
b            2348    2542     38.9    19.50 +/- 0.31
b            2696    2716     19.5    19.09 +/- 0.34
u            2323    2517     38.9    18.77 +/- 0.26
u            2671    2691     19.5   >18.89
uvw1         2299    3576     92.8   >19.63
uvm2         2446    3536    235.6   >19.89
uvw2         2397    2592     38.9   >18.84
====================================================

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.03 mag (Schlegel et al.,
1998, ApJS, 500, 525).  The photometry is on the UVOT photometric
system described in Poole et al. (2008, MNRAS, 383,627).