GCN Circular 41969
Subject
GRB 250924A: Mondy optical observations, afterglow fading
Event
Date
2025-09-24T16:19:46Z (a month ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), E. Klunko (ISTP) report on behalf of GRB-IKI-FuN:
We observed the field of GRB 250924A detected by Swift (Siegel et. al, GCN 41897) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy). We are obtaining the images of the GRB field in the R-filter. The optical afterglow initially detected by Swift/UVOT (Siegel et. al, GCN 41897) and further observed by (Becerra et. al, GCN 41960; Schneider et. al, GCN 41963; Freeberg et. al, GCN 41968) is clearly visible in the stacked image of first 10 obtained images. Preliminary photometry is as follows:
Date UTstart Exptime t-T0 Filter OT Err. UL
(nxs) (mid, days) (3sigma)
2025-09-24 14:37:48 10x120 0.27036 R 21.47 0.09 22.5
The photometry was calibrated against nearby USNO-B1.0 stars (R2-mags) and not corrected for the Galactic extinction. We note that the afterglow has faded at ~3.7 mag in ~6.5 hr since detection. Further observations are ongoing.