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GRB 260924A: Ondrejov D50 optical afterglow detection
GCN Circulars —

GCN Circular 45743
GRB 260924A: Ondrejov D50 optical afterglow detection
From: Filip Novotný at Masaryk University
Issued: 2026-09-25 12:06 UTC
Type: GRB, Afterglow, Optical Transient

F. Novotny, J. Strobl, M. Jelinek and R. Hudec (ASU CAS Ondrejov) report:

We observed the position of GRB 260924A (D'Elia et al., GCN 45713;
Evans et al., GCN 45715), detected by Swift (trigger=1513082), with the
D50 telescope of the Astronomical Institute Ondrejov, near Prague, Czech
Republic. We obtained 14x120s and 10x60s Sloan r'-band exposures between
03:15 and 03:57 UT on 2026 September 25, i.e. 26.0-26.7 h after the
trigger.

The optical afterglow (Hu et al., GCN 45717; Izzo et al., GCN 45718)
is detected in the combined image (mean epoch T0+26.4 h) at
RA, Dec = 08:55:03.11, +12:02:35.5 (J2000), consistent with the UVOT
position (Klingler et al., GCN 45735), with a magnitude of

r' = 19.12 +/- 0.08 (AB)

Photometry is calibrated in Sloan r' (AB system) against ATLAS-RefCat2
field stars, not corrected for Galactic extinction (E(B-V)=0.041 mag).

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.

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