TITLE:   GCN CIRCULAR
NUMBER:  35458
SUBJECT: GRB 240101B: Swift/UVOT Upper Limits
DATE:    24/01/02 12:11:38 GMT
FROM:    Paul Kuin at MSSL <npkuin@gmail.com>

N. P. M. Kuin (UCL-MSSL) and S. B. Cenko (GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 240101B
110 s after the BAT trigger (Cenko et al., GCN Circ. 35449).
No optical afterglow consistent with the XRT position
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           134          284          147         >21.1
u_FC               294          543          246         >20.1
white              134         1718          411         >21.8
v                  110         1595          130         >19.2
b                  549         1693          117         >20.5
u                  294         1669          343         >20.2
w1                 675         1644          117         >19.3
m2                 648         1619           97         >21.0
w2                 599         1741          134         >19.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.287 in the direction of the burst
(Schlegel et al. 1998).