GCN Circular 41264
Subject
GRB 250806A: Swift/UVOT U-band detection
Event
Date
2025-08-07T11:15:10Z (18 days ago)
From
Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>
Via
email
A.A. Breeveld (UCL-MSSL) and Paul Kuin (UCL-MSSL) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of the SVOM/ECLAIRS detected burst GRB 250806A (Xie et al., GCN Circ. 41243) 354 s after the SVOM trigger. The X-ray afterglow reported by Campana et al. (GCN Circ. 41249) and Liang et al. (GCN Circ. 41260) is detected in the initial U-band exposure, but has faded in the later white band exposures.
Preliminary magnitude and 3-sigma upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures is:
Filter T_start(s) T_stop(s) Exp(s) Mag
u 354 1370 1000 20.5 ± 0.3
white 63123 64122 975 > 21.7
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V)=0.044 in the direction of the burst (Schlegel et al. 1998).