GCN Circular 3050

T. Poole (MSSL), C. Gronwall (PSU), A. Blustin (MSSL), P. Brown (PSU), S. 
Rosen, K. McGowan, M. De Pasquale (MSSL), P. Boyd (GSFC/UMBC), S. Holland, 
M. Still (GSFC/USRA), W. Landsman (GSFC), S. Hunsberger (PSU), A. Breeveld 
(MSSL), P. Roming (PSU), K. Mason, P. Schady (MSSL), M. Ivanushkina (PSU), 
T. Kennedy, P. Smith, B. Hancock (MSSL), S. Koch (PSU), M. Carter, H. 
Huckle (MSSL),  P. Broos, J. Racusin (PSU), E. Fenimore (LANL),
B. Zhang (UNLV), J. Nousek (PSU), N. Gehrels (GSFC), on behalf of the 
Swift UVOT team.

The Swift Ultra-Violet/Optical Telescope (UVOT) began observations of
GRB050219b on February 19, 2005, at 12:57:51 UT, 52 minutes after the
initial Swift BAT trigger (Cummings et al, GCN 3044
Not found
 
 
). The delay in
observations was due to the Earth-limb constraint, which prevented an
immediate slew.  We detect no source at the Swift XRT position (Burrows et
al, GCN 3043
Not found
 
 
).  The limiting magnitudes (3-sigma) in each of the UVOT
filters are as follows:

A re-examination of the UVOT data at the new XRT position (Racusin et al, 
GCN 3049
Not found
 
 
) revealed no new source detection down to the following 3-sigma 
limiting magnitudes

Filter	Lim_Mag  Duration   T_start
   UVW2	~ 22.16	  1154	     T+3120
   UVM2	~ 22.24   1435	     T+3243
   UVW1	~ 22.23   940	     T+3349
   U	~ 20.74   100	     T+3455
   B	~ 20.9    100	     T+3561
   V	~ 19.41   100	     T+3136

Several exposures were taken in the UV filters, and these were co-added in 
order to derive the limiting magnitudes. This is the cause of the apparent 
overlap between the duration of these exposure and the start time of the 
exposures in the optical filters.

We caution that the instrument is not yet fully calibrated and that the
magnitude limits presented here may need to be refined.