GCN Circular 41981
Subject
GRB 250924A: SAO RAS optical observations
Event
Date
2025-09-25T10:53:27Z (9 months ago)
From
Alexander Moskvitin at SAO RAS <mosk@sao.ru>
Via
Web form
A. Moskvitin (SAO), V. Goranskij (SAI MSU), N. Pankov (HSE),
A. Pozanenko (IKI) report on behalf of GRB follow-up collaboration
and IKI-GRB-FuN.
We observed the field of the GRB 250924A (Siegel et. al, GCN 41897;
Osborne et. al, GCN 41973; Campana et. al, GCN 41974) with two SAO RAS
telescopes, 1-m Zeiss-1000 equipped with the CCD-photometer on
September 24/25, 23:41:32--00:27:16, and 6-m BTA equipped
with the focal reducer SCORPIO-2 (Afanasiev & Moiseev, 2011, BaltA,
20, 363) on September 25, 01:42:55--01:58:24 UT.
The optical transient (Siegel et. al, GCN 41959; Becerra et. al,
GCN 41960; Schneider et. al, GCN 41963; Freeberg et. al, GCN 41968;
Pankov et. al, GCN 41969; Zheng and Filippenko, GCN 41970;
Siegel, GCN 41975; Ma et al., GCN 41976; Cotter et al., GCN 41980;
and also observed in NIR, Mo et. al, GCN 41972) is clearly detected
in our stacked frames. Preliminary results are as following.
Date UTstart Exptime t-T0 Filter OT Err. UL Tel.
s (mid, days) (3sigma)
2025.09.24 23:41:32 2520 0.65689 Rc 23.18 +/- 0.24 23.5 1-m
2025.09.25 01:42:55 600 0.73068 Rc 23.07 +/- 0.10 24.3 6-m
The photometry calibrated against nearby USNO-B1.0 stars (R2 magnitudes)
and not corrected for the Galactic extinction.