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GCN Circular 6336

Subject
GRB070420: Swift UVOT continuing observations
Date
2007-04-20T16:57:52Z (17 years ago)
From
Stefan Immler at NASA/GSFC <immler@milkyway.gsfc.nasa.gov>
S. Immler (USRA/GSFC), F. E. Marshall (NASA/GSFC), S. T. Holland
(CRESST/USRA/GSFC), and M. Stamatikos (NASA/ORAU) report on
behalf of the Swift/UVOT team:

The UVOT position sent out as a GCN notice gave an invalid position while
GCN 6330 had the correct position. We regret any confusion this might have
caused. The revised UVOT position of the afterglow is
RA(J2000) = 08h04m55.17s, Dec(J2000) = -45d33'20.0".
We estimate a statistical accuracy of 0.2 arcsec radius (90% confidence)
but with a systematic uncertainty of the aspect solution of about 0.5 
arcsec.

The Swift/UVOT began taking data in the field of GRB070420 90s after
the BAT trigger (Stamatikos et al., GCN 6330). The afterglow is detected
in all UVOT optical filters. The large reddening, E(B-V) = 0.52, might 
explain
the non-detection in the UV. The flux is decaying with t**-0.7 in the White
for times between T+500 and T+10000 seconds. The photometry results are
given for the 7 UVOT filters below.

V                T+(s)          Exp(s)       Mag

White          109            99           17.4+/-0.1
                  7125           197          20.8+/-0.1
V                    90           10            17.9+/-0.1
B                  693          10            18.8+/-0.1
U                  669          20            21.1+/-0.1
UVW1         645          20            >20.4 (3-sigma)
UWM2         620          20            >20.8 (3-sigma)
UVW2             723          20            >20.8 (3-sigma)
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