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GCN Circular 10285

Subject

GRB 091221: UVOT Confirmation of an Optical Afterglow

Date

2009-12-21T22:12:23Z (15 years ago)

From

Stephen Holland at USRA/NASA/GSFC/SSC <Stephen.T.Holland@nasa.gov>

S. T. Holland (CRESST/GSFC/USRA), M. de Pasquale (MSSL),
P. Kuin (MSSL), and H. A. Krimm (CRESST/GSFC/USRA)
report on the behalf of the Swift/UVOT team:

       The Swift/UVOT observed the field of GRB 091221 (Krimm et
al. 2009, GCN Circ. 10283Not found
 
 
) starting approximately 80 s after the BAT
detection.  We confirm the optical afterglow detected by Krimm et
al. 2009, GCN Circ 10283Not found
 
 
 and Zheng et al. 2009, GCN Circ. 10284Not found
 
 
.  The
preliminary UVOT position is

     RA =  03:43:11.47 =  55.79771 deg
    Dec = +23:14:28.9  = +23.24136 deg

with a preliminary error estimate of 0.6 arcsec (radius, 90%
containment).  The preliminary white magnitude is

Filter     TSTART     TSTOP     EXPOSURE        Mag   Err
---------------------------------------------------------
White          80       230          150      20.22  0.28
---------------------------------------------------------

The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight corresponding to a
reddening of E_{B-V} = 0.22 mag (Schlegel et al., 1998, ApJS, 500,
525).  All photometry is on the UVOT photometry system described in
Poole et al. (2008, MNRAS, 383, 627).