TITLE:   GCN CIRCULAR
NUMBER:  9948
SUBJECT: GRB090926A: Swift/UVOT observations
DATE:    09/09/27 12:41:56 GMT
FROM:    Samantha Oates at MSSL  <sro@mssl.ucl.ac.uk>

S. R. Oates (MSSL-UCL) and L. Vetere (PSU) report on behalf
of the Swift/UVOT team:

The Swift/UVOT began observerving the field of Fermi GRB 090926A
47ks after the Fermi  GBM and LAT trigger (Bissaldi., GCN Circ. 9933;
Uehara ., GCN Circ. 9934). We detect a fading optical afterglow in  
white,
v and u filters at the position reported by UVOT (Gronwall et al.,
GCN Circ. 9938) and Skynet/PROMPT (Haislip et al., GCN Circ 9937).
The lightcurve appears to rebrighten from 70ks to the end of
current observations.

Preliminary magnitudes are reported below.

Filter  T_start(s) T_stop(s)  Exposure      Mag  Err
-------------------------------------------------------
white     46977     47341      358       18.71 +/- 0.04
white     69902     70369      459       19.32 +/- 0.05
v         47348     47712      358       18.45 +/- 0.16
u         46608     46972      358       18.21 +/- 0.07
u         69429     69896      459       18.85 +/- 0.09
u         86050     86613      554       18.52 +/- 0.07
-------------------------------------------------------

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.02 mag (Schlegel et al.,
1998, ApJS, 500, 525).  The photometry is on the UVOT flight system
described in Poole et al. (2008, MNRAS, 383,627).