GCN Circular 41938
Subject
GRB 250916A: Swift/UVOT Detection
Event
Date
2025-09-22T15:32:00Z (a year 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 the Fermi/GBM detected burst GRB 250916A 102120s after the trigger (Fermi GBM team, GCN Circ. 41839).
The optical counterpart detected by Belkin et al., GCN Circ. 41847; Mohan et al., GCN Circ. 41858; Moskvitin et al., GCN Circ. 41859; Burkhonov et al., GCN Circ. 41860; de Ugarte Postigo et al., GCN Circ. 41863; Moskvitin et al., GCN Circ. 41870; Zheng and Filippenko, GCN Circ. 41873; Pankov et al., GCN Circ. 41892; Hall et al., GCN Circ. 41921 and Moskvitin et al., GCN Circ. 41934, is detected in the initial white and u-band UVOT exposures.
Preliminary magnitudes and upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
u 102120 107275 968 20.5 ± 0.2
white 102446 102767 316 21.1 ± 0.3
v 102774 103051 273 >19.4
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.051 in the direction of the burst (Schlegel et al. 1998).