TITLE:   GCN CIRCULAR
NUMBER:  24747
SUBJECT: GRB190604B: Swift/UVOT detection
DATE:    19/06/04 20:40:46 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) 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 190604B 
128 s after the BAT trigger (Page et al., GCN Circ. 24742). A faint 
source is detected in the initial white UVOT exposure at a position 
consistent with the enhanced XRT source position (Evans et al., GCN 
Circ. 24746).

The preliminary detection and 3-sigma upper limits using the UVOT 
photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for 
the early exposures are:

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

white     	128      276         146        19.90 ± 0.24
white     	618      812          39        >19.63
v         	669      861          39        >17.95
b         	594      787          39        >18.98
u         	338      588         246        >19.71
uvw1      	718      738          20        >17.44
uvw2      	645      837          39        >18.09

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.15 in the direction of the 
  burst (Schlegel et al. 1998).