GCN Circular 41864
Subject
GRB 250917B: Swift/UVOT Upper Limits
Event
Date
2025-09-18T11:35:38Z (3 days ago)
From
Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>
Via
email
A.A. Breeveld (UCL-MSSL) and R. Caputo (GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250917B 139 s after the Swift/BAT trigger (Caputo et al., GCN Circ. 41848) and the Fermi GBM trigger (Fermi GBM Team, GCN 41846).
No optical afterglow consistent sources 1, 5 or 6 identified by the Swift-XRT (Kennea et al., GCN Circ. 41851) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 139 289 147 >20.5
u_FC 351 601 246 >19.9
white 139 5391 492 >21.2
v 681 1059 39 >18.1
b 606 5225 236 >20.1
u 351 5020 462 >20.1
w1 730 4815 216 >18.9
m2 705 1084 39 >18.8
w2 831 1035 39 >19.0
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.983 in the direction of the burst (Schlegel et al. 1998).