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GCN Circular 9067

Swift/UVOT detection of GRB090401B
2009-04-01T09:39:08Z (15 years ago)
Patricia Schady at MSSL/Swift <>
P.Schady (MSSL-UCL) and S.R.Oates report on behalf of the Swift/UVOT  

Following from the tentative UVOT afterglow detection of GRB090401B  
reported in Schady et al. (GCN 9066), we here report a fading by over  
two magnitudes between the two UVOT white finding charts, taken 792s  
apart at the following position

RA (J2000) = 06:20:21.11 (95.08775deg)
Dec (J2000) = -08:58:19.5 (-8.97199deg)

with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence),  
suggesting this to be the optical afterglow of GRB090401B. This  
position falls on a known source, making absolute magnitudes and a  
precise localisation difficult at this stage, and further data will be  
required in order to carry out source subtraction.

The values quoted above are not corrected for the Galactic extinction  
due to the reddening of E(B-V)  = 0.67 in the direction of the burst  
(Schlegel et al. 1998). All photometry is on the UVOT photometry  
system described in Poole et al. (2008, MNRAS, 383, 627).
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