TITLE:   GCN CIRCULAR
NUMBER:  40981
SUBJECT: GRB 250704A: Swift/UVOT Detection
DATE:    25/07/05 18:25:39 GMT
FROM:    Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>

M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 250704A 2.9 ks after the SVOM/ECLAIRs trigger (Cao et al., GCN Circ. 40934). A source consistent with the XRT position (Osborne et al., GCN Circ. 40950) and the optical transient (Schneider et al., GCN Circ. 40953; Cao et al., GCN Circ. 40964) is detected in the UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  01:08:44.62 =  17.19427 (deg.)
    Dec (J2000) = -17:19:26.3  = -17.32398 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).

Preliminary detections 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

u                 2933         8704         1993      18.38+/-0.05
u                70704        76996         2879      20.77+/-0.28

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.015 in the direction of the burst
(Schlegel et al. 1998).