TITLE:   GCN CIRCULAR
NUMBER:  9758
SUBJECT: GRB090809: Swift/UVOT observations
DATE:    09/08/10 05:37:54 GMT
FROM:    Wayne Landsman at GSFC/SSAI  <wayne.b.landsman@nasa.gov>

W.B. Landsman (NASA/GSFC) and C. Markwardt (CRESST/GSFC/UMD) report on 
behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 090809 
108s after the BAT trigger (Markwardt et al., GCN Circ. 9754),      The 
tentative UVOT detection reported by Markwardt et al. is confirmed 
following the downlink of additional data.   The UVOT position 
determined from the white finding chart exposure is

RA (J2000)  21:54:43.19   =  328.679938 (deg)
Dec (J2000) -00:05:1.83   =  -0.083842 (deg)

with an estimated uncertainty of 0.6 arcsec (radius, 90% confidence,  
statistical + systematic), consistent with the NOT afterglow position 
(Xu et al., GCN Circ. 9755).

The initial magnitudes and upper limits are as follows:

Filter   T_start(s) Tstop(s) Exp(s)      Mag
white        108    194      84     19.53 +/- 0.14
white       3396   3545     147     21.03 +/- 0.33

v           3552   5181     393     19.87 +/- 0.30
b           4365   5976     367    >21.1  (3 sigma)
u           4162   5796     391    >20.8  (3 sigma)
uvw1        3962   5592     393    >20.7  (3 sigma)
uvm2        3757   5386     393    >20.5  (3 sigma)
uvw2        4776  10964    1082    >21.6  (3 sigma)

The values quoted above are not corrected for the Galactic extinction 
due to the reddening of E(B-V) = 0.10 in the direction of the burst 
(Schlegel  et al. 1998). The photometry is on the UVOT photometric 
system described in Poole et al. (2008, MNRAS, 383, 627).