TITLE:   GCN CIRCULAR
NUMBER:  27648
SUBJECT: GRB 200424A: Swift/UVOT Upper Limits
DATE:    20/04/25 23:20:23 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

N. P. M. Kuin (UCL-MSSL) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the INTEGRAL GRB 200424A
(Mereghetti et al. GCN Circ. 27634) between T0+17 ks and T0+31 ks,
where T0 = 2020-04-24 12:06:45 UT.
We report here the UOT results for source #1 found by the Swift/XRT
(D'Avanzo et al., GCN Circ. 27640).

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(ks)   T_stop(ks)      Exp(s)         Mag

v                   18           30          236         >19.1
b                   17           30          236         >20.2
u                   17           30          236         >19.9
w1                  17           30          492         >19.9
m2                  17           31         2678         >20.8
w2                  17           30          944         >20.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998).