TITLE:   GCN CIRCULAR
NUMBER:  9527
SUBJECT: GRB090618: Swift/UVOT bright afterglow detection
DATE:    09/06/18 19:00:10 GMT
FROM:    Patricia Schady at MSSL/Swift  <ps@mssl.ucl.ac.uk>

P. Schady (MSSL-UCL) reports on behalf of the Swift UVOT team:

The Swift/UVOT began settled observations of the field of GRB 090618 129s 
after the BAT trigger (Schady et al., GCN Circ. 9512) and a 
decaying source is detected in all UVOT filters at the position reported 
in Schady et al. (GCN Circ. 9512), consistent with refined XRT error 
circle (Evans et al., GCN Circ. 9521) as well as the optical afterglow 
position reported in a number of other GCNs (GCN Circ. 9512, 9514, 9515). 
The detection of the afterglow of GRB 090618 in all filters puts an upper 
limit on the redshift of z < 1.7, consistent with the redshift constraints 
reported by Cenko et al. (GCN Circ. 9518).

The magnitudes for the first UVOT observation of GRB 090618 in each filter 
are as follows:

Filter  T_start(s)  T_stop(s)  Exp(s)      Mag
white      129        279       147    14.27+/-0.01
v          671        691       19     15.60+/-0.09
b          596        616       19     15.92+/-0.06
u          340        590       246    14.62+/-0.01
uvw1       720        740       19     15.09+/-0.08
uvm2       695        715       19     15.23+/-0.12
uvw2       647        667       19     15.27+/-0.10

The values quoted above are not corrected for the Galactic extinction due 
to the reddening of E(B-V) = 0.09 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).