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GCN Circular 6238

Subject
UVOT observations of GRB070330
Date
2007-03-31T21:18:15Z (17 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
N.P.M. Kuin (MSSL-UCL), D. Grupe (PSU), P. Brown (PSU) report
on behalf of the Swift/UVOT team:

The Swift/UVOT began taking data in the field of GRB070330 54s after the BAT 
trigger (Grupe et al., GCN 6232). The afterglow is only detected in the first 
UVOT V exposure, with a magnitude of V=18.69+/-0.24, after which the afterglow 
had decayed below the UVOT detection threshold, suggesting a decay rate of 
alpha_V > 0.8. The refined UVOT afterglow position is
RA (J2000)  = 17:58:09.98 (269.5426)
Dec (J2000) = -63:47:34.80 (-63.7930)
We note that the refined position is 0.5" away from the preliminary UVOT 
position reported in GCN 6232. The photometry results are given below for the 5 
UVOT filters in which observations were made. Due to the presence of a bright 
star no observations could be obtained in the UVW2 and white filters.

Filter  Mid_T(s)   Exp(s)  Mag
V       266        393     18.69+/-0.24
V       33978      1632    > 21.45 (3-sigma upper limit)
M2      25521      2814    > 18.35 (3-sigma upper limit)    `
W1      20282      1998    > 18.36 (3-sigma upper limit)
U       25521      2814    > 21.60 (3-sigma upper limit)
B       30318      3305    > 18.15 (3-sigma upper limit)

Mid_T is the weighted mid time of the exposure since the BAT trigger. These 
magnitudes are not corrected for the expected reddening of E(B-V)=0.063.

For the time being it is not possible to provide a redshift given the low 
signal-to-noise ratio of the data. Further analysis is ongoing. A high (~4) 
redshift is possible and we encourage further ground follow-up.

[GCN OPS NOte(25aug07): Per UVOT Team request, the Mid_T value
for the first V exposure ws changed from 462 to 266. Acknowledgements
to F. Marshall.]
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