TITLE:   GCN CIRCULAR
NUMBER:  27643
SUBJECT: GRB 200425A: Swift/UVOT Upper Limits
DATE:    20/04/25 13:23:07 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

N. P. M. Kuin (UCL-MSSL) and M. G. Bernardini (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 200425A 94 s after the BAT trigger (Bernardini et al.,
GCN Circ. 27638). No optical afterglow consistent with the
XRT position (Bernardini et al. GCN Circ. 27638)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            94          244          147         >20.7
u_FC               253          503          246         >19.9
white               94          728          186         >20.5
v                  585          778           39         >18.6
b                  510          704           39         >19.1
u                  253          679          265         >19.9
w1                 635          827           39         >18.4
m2                 610          802           39         >18.9
w2                 560          753           39         >18.7

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.16 in the direction of the burst
(Schlegel et al. 1998).