GCN Circular 45735
GRB 260924A: Swift/UVOT Detection
From: unknown
Issued: 2026-09-25 01:37 UTC
Type: GRB, Optical Transient

N. Klingler (NASA-GSFC / UMBC / CRESST II) and V. D'Elia (SSDC & INAF-OAR) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 260924A 158 s after the BAT trigger (D'Elia et al., GCN Circ. 45713). A source consistent with the XRT position (Evans et al., GCN Circ. 45715) is detected in the initial UVOT exposures.

The preliminary UVOT position is:
RA (J2000) = 08:55:03.13 = 133.76304 (deg.)
Dec (J2000) = +12:02:35.4 = 12.04318 (deg.)
with an estimated uncertainty of 0.50 arc sec. (radius, 90% confidence).

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

white 158 308 147 14.68 +/- 0.02
v 4254 4454 197 15.11 +/- 0.03
b 3637 3837 197 15.71 +/- 0.03
u 334 372 37 17.33 +/- 0.24
w1 4664 4864 197 >18.5
m2 4459 4658 197 >19.2
w2 4048 4247 197 >19.2

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.041 in the direction of the burst (Schlegel et al. 1998).

Filter: gamma-ray bursts are posted only if in the top 10% of the past year's — by fluence (total energy received per cm², from Fermi GBM, Konus-Wind, GECAM and similar circulars; now ≥ 3.9×10^-5 erg/cm²) or by the number of GCN Circulars about the burst (now ≥ 14). Thresholds are recalculated monthly.
Relayed automatically from NASA's General Coordinates Network.