TITLE:   GCN CIRCULAR
NUMBER:  9544
SUBJECT: GRB 090621: Swift/UVOT Upper Limits
DATE:    09/06/21 12:29:18 GMT
FROM:    Peter Curran at MSSL  <pac@mssl.ucl.ac.uk>

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


The Swift/UVOT began settled observations of the field of GRB 090621
123 s after the BAT trigger (Curran et al., GCN 9540). No optical
afterglow consistent with the refined XRT position (Page et al., GCN 
9543) is detected in the initial UVOT exposures. Preliminary 3-sigma 
upper limits using the UVOT photometric system (Poole et al. 2008, 
MNRAS, 383, 627) for the first exposures are:


Filter         T_start(s)  T_stop(s)  Exp(s)     Mag

wh             123         7115       805        >21.5
v              613         6089       333        >19.4
b              538         6910       310        >20.5
u              282         6705       736        >20.5
uw1            662         6500       320        >19.8
um2            637         6295       333        >19.7
uw2            588         5884       333        >19.9


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).