TITLE:   GCN CIRCULAR
NUMBER:  36197
SUBJECT: GRB 240419B: Swift/UVOT Upper Limits
DATE:    24/04/20 15:20:59 GMT
FROM:    Sam Shilling at Lancaster University <shilling.sam@gmail.com>

S. P. R. Shilling (Lancaster U.), S. R. Oates (Lancaster U.),
A. A. Breeveld (UCL-MSSL), N. P. M. Kuin (UCL-MSSL) and S. Dichiara (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 240419B
159 s after the BAT trigger (Dichiara et al., GCN Circ. 36180).
No optical afterglow consistent with either the enhanced XRT position
(Osborne et al., GCN Circ. 36186) or the NOT optical afterglow position
(Malesani et al., GCN Circ. 36191) 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) exposures and subsequent exposures are:

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

white_FC           159          308          147         >20.3
u_FC               317          567          246         >19.5
white              159          790          186         >20.4
v                  647          667           19         >17.3
b                  572          765           39         >18.6
u                  317          741          265         >19.5
w1                 696          716           19         >17.5
m2                 672          691           19         >17.2
w2                 623          643           19         >17.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.077 in the direction of the burst
(Schlegel et al. 1998).