GCN Circular 41721
Subject
GRB 250904A: Swift/UVOT Detection
Event
Date
2025-09-05T10:09:45Z (8 days ago)
From
Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>
Via
email
S. R. Oates (Lancaster Uni.) and C. Salvaggio (INAF-OAB)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250904A
86 s after the BAT trigger (Salvaggio et al., GCN Circ. 41704).
A source consistent with the XRT position (Goad et al., GCN Circ. 41711)
is detected in white and marginally in u.
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/3sigUL
white (FC) 86 235 147 20.23+\-0.36
u (FC) 298 441 141 19.14+\-0.41 (2.7 sigma)
white 4990 10603 1097 20.60+\-0.16
v 5401 5601 197 >19.5
b 4786 6421 393 >20.4
u 6016 6215 197 >19.6
uvw1 5811 6011 197 >19.5
uvm2 5606 5806 197 >19.4
uvw2 5196 10942 524 >20.2
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.284 in the direction of the burst
(Schlegel et al. 1998).