GCN Circular 8703

N. P. M. Kuin (MSSL/UCL) and E. A. Hoversten (PSU) report
on behalf of the Swift UVOT team.

The Swift UltraViolet/Optical Telescope (UVOT) began settled
observations of GRB081221 (Swift BAT trigger number 337889,
Hoversten et al., GCN Circ.  8687
Not found
 
 
), on December 21, 2008, at
16:22:29, 78 seconds after the trigger with a white finding chart.

We do not detect any new source at the enhanced XRT position
reported in GCN Circ. 8690
Not found
 
 
 (Evans et al.).

The observed magnitude upper limits for GRB 081221 are given below
for the first observations and the summed exposures in the UVOT
filters:

Filter Tstart(s) Tstop(s)  Exp(s)  Magnitude

wh       78       228     149.8    >20.84  (3-sigma UL)
v       619       639      19.4    >17.89  (3-sigma UL)
b       545       565      19.4    >18.85  (3-sigma UL)
u       290       540     245.8    >20.15  (3-sigma UL)
uvw1    668       688      19.4    >18.10  (3-sigma UL)
uvm2    644       664      19.5    >17.71  (3-sigma UL)
uvw2    595       615      19.4    >18.08  (3-sigma UL)

wh       78      6086     381.0    >21.41  (3-sigma UL)
v        59     34696    2192.4    >20.74  (3-sigma UL)
b       545     41269    1765.2    >21.55  (3-sigma UL)
u       290     40478    3667.7    >21.69  (3-sigma UL)
uvw1    668     39565    3758.4    >21.57  (3-sigma UL)
uvm2    644     45178    3409.4    >21.55  (3-sigma UL)
uvw2    595     33783    2005.6    >21.35  (3-sigma UL)

The values quoted above are on the UVOT Photometric System
(Poole et al, 2008, MNRAS 383,627). They are not corrected for the
expected galactic reddening of E(B-V) = 0.021 in the direction of
the burst (Schlegel et al. 1998).