GCN Circular 10289

M. De Pasquale (MSSL/UCL) and H. Krimm (CRESST/GSFC/USRA)
report on behalf of the Swift/UVOT team:

  The Swift/UVOT began settled observations of the field of GRB091221
80s after the BAT trigger with a 150s finding chart exposure in
the White filter.

  We detect the optical afterglow in the finding chart exposure.
The refined UVOT position is RA = 55.79750, Dec = 23.24119 (J2000), 
corresponding to

             RA = 03h 43m 11.40s,
             Dec = +23d 14m 28.3s (J2000)

with an estimated uncertainty of 0.6 arcsec (radius, 90% confidence).
This position is consistent with the XRT enhanced position (Evans
et al., GCN 10287
Not found
 
 
) and ground-based detections (Zheng et al., GCN
10284
Not found
 
 
; Klose et al., GCN 10286
Not found
 
 
).

  The afterglow is not detected anymore in single or summed exposures
in all filters. Preliminary magnitudes and 3 sigma upper limits
are reported below.

Filter    T_start(s) T_stop(s)  Exposure(s)    Mag  Err
-----------------------------------------------------------------------
white        80        230       149.8       20.19 +/- 0.27
white      3657      11605       927.1          >21.62
v          4068       5704       393.2          >19.56
b          3452      11054      1278.4          >21.11
u          4683      10142      1083.4          >20.68
uvw1       4478       6075       354.4          >19.96
uvm2       4273       5909       393.3          >19.79
uvw2       3863       5499       393.3          >20.07
------------------------------------------------------------------------

The values quoted above are not corrected for the heavy Galactic 
extinction corresponding to the reddening of E(B-V) = 0.22 in the 
direction of the burst (Schlegel et al. 1998, ApJS, 500, 525). The 
photometry is on the UVOT photometric system described in Poole et al. 
(2008, MNRAS, 383, 627).

[GCN OPS NOTE(22dec09): Per author's request, the Subject-line
was changed from 091208B to 091221.]