GCN Circular 41316
Subject
GRB 250809A: Swift/UVOT Detection
Event
Date
2025-08-10T16:51:32Z (2 months ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
Via
email
N.P.M. Kuin (UCL/MSSL) and T. M. Parsotan (GSFC) report on behalf of the
Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250809A
128 s after the BAT trigger (Parsotan et al., GCN Circ. 41303). A source
consistent with the XRT position ( Evans et al. GCN Circ. 41304 ) is
detected in the initial UVOT exposures.
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
v 435 755 58 17.62 +/- 0.21
b 384 1038 97 18.86 +/- 0.19
u 128 1013 452 19.57 +/- 0.21
w1 484 805 58 >18.4
m2 459 780 58 >20.1
w2 410 1064 78 >18.8
The earliest exposures were fainter; these detections are near the peak of
the light curve.
The magnitudes in the table are not corrected for the Galactic extinction due
to the reddening of E(B-V) = 1.919 in the direction of the burst (Schlegel
et al. 1998).