GCN Circular 40981
Subject
GRB 250704A: Swift/UVOT Detection
Event
Date
2025-07-05T18:25:39Z (13 days ago)
From
Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>
Via
Web form
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).