TITLE:   GCN CIRCULAR
NUMBER:  34008
SUBJECT: GRB 230618A: Swift/UVOT Upper Limits
DATE:    23/06/18 17:05:34 GMT
FROM:    Paul Kuin at MSSL <npkuin@gmail.com>

N.P.M. Kuin (MSSL/UCL) 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 230618A
137 s after the BAT trigger (Page et al., GCN Circ. 33989).
No optical afterglow consistent with the XRT position (Evans GCN
Circ. 33990) is detected in the initial UVOT exposures. The source
was however detected in r and i (Strausbaugh et al, GCN Circ. 33992 and KAIT
(Zhang and Filipenko, GCN Cric. 34001) in clear (R).
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           137          287          147         >20.4
u_FC               296          546          246         >19.9
white              137         1022          295         >20.7
u                  296          546          246         >19.9
w1                5114         5178           63         >18.9
m2                4909         5108          197         >19.7

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.025 in the direction of the burst
(Schlegel et al. 1998).