TITLE:   GCN CIRCULAR
NUMBER:  33576
SUBJECT: GRB 230405B: Swift/UVOT Upper Limits 
DATE:    23/04/06 08:06:53 GMT
FROM:    Samantha Oates at MSSL  <samantha.oates@alumni.ucl.ac.uk>

S. R. Oates (U. Birmingham) and K. L. Page (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 230405B
75 s after the BAT trigger (Page et al., GCN Circ. 33571).
No optical afterglow consistent with the XRT position
(Beardmore et al. GCN Circ. 33574)
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

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

white_FC            75          224          147         >20.5
u_FC               287          537          246         >19.7
white               75         1363          373         >20.7
v                  618         4860          274         >19.1
b                  542         1339           78         >19.0
u                  287         1313          304         >19.7
w1                 668         1289           78         >18.5
m2                 642         5065          274         >19.4
w2                 593         1389           97         >18.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.166 in the direction of the burst
(Schlegel et al. 1998).