TITLE:   GCN CIRCULAR
NUMBER:  9774
SUBJECT: GRB090812: Swift/UVOT observations
DATE:    09/08/12 13:52:31 GMT
FROM:    Patricia Schady at MSSL/Swift  <ps@mssl.ucl.ac.uk>

P. Schady (MSSL-UCL) and M. Stamatikos (NASA/ORAU) report on behalf of the 
Swift UVOT team:

The Swift/UVOT began settled observations of the field of GRB 090812 86s 
after the BAT trigger (Stamatikos et al., GCN Circ. 9768). An 
uncatalogued, fading source is detected in the UVOT white, v, b and u band 
filters at the position reported in Stamatikos et al. (GCN Circ. 9768), 
consistent with the refined XRT error circle (Goad et al., GCN Circ. 
9772). The detection of the afterglow in the white, v, b and u filters is 
consistent with the spectroscopic redshift of z=2.452 reported by Ugarte 
Postigo et al. (GCN Circ. 9771). Early time UVOT obserations indicate a 
decay rate of alpha~1.5.

The magnitudes and 3-sigma upper limits for the UVOT observations of GRB 
090812 in each filter are as follows:

Filter  T_start(s)  T_stop(s)  Exp(s)  Mag/3-sig UL
white      86         235       146    17.35+/-0.03
v          628        647       19     18.17+/-0.41
b          554        573       19     18.62+/-0.28
u          299        548       246    18.65+/-0.11
uvw1       677        1124      58     > 19.20
uvm2       652        1099      58     > 18.72
uvw2       603        1050      58     > 19.13

The values quoted above are not corrected for the Galactic extinction due 
to the reddening of E(B-V) = 0.02 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).