GCN Circular 41920
Subject
GRB 250920C: Swift/UVOT Detection
Event
Date
2025-09-20T21:48:29Z (21 hours ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
Via
email
N. P. M. Kuin (UCL-MSSL) and R. Gupta (GSFC) report on behalf of the
Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250920C 124 s
after the BAT trigger (Gupta et al., GCN Circ. 41904). A source consistent
with the XRT position is detected in the initial UVOT exposures.
The preliminary UVOT position is:
RA (J2000)= 03h 25m 51.76s, 51.46568 deg
Dec (J2000) = -29d 39m 20.2s, -29.65562 deg
consistent with the detection by GOTO (Wortley et al. GCN Circ. 41907).
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 146 207 60.5 14.55 +/- 0.04
v 124 133 10.1 14.56 +/- 0.09
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.019 in the direction of the burst
(Schlegel et al. 1998).