GCN Circular 46001
Subject
GRB 261017A: SAO RAS optical upper limit
Event
Date
2026-10-20T22:33:10Z (19 days ago)
From
Alexander Moskvitin at SAO RAS <mosk@sao.ru>
Via
email
A. Moskvitin (SAO), V. Vlasyuk (SAO), A. Volnova (IKI),
N. Pankov (IKI) and A. Pozanenko (IKI) on behalf of the SAO GRB
follow-up team and the IKI-GRB-FuN report.
We observed the field of GRB 261017A detected by Fermi, Swift
and Konus-Wind (The Fermi GBM team, GCN 45973; Siegel et al.,
GCN 45974; Mukherjee et al., GCN 45976; Beardmore et al., GCN 45977;
Sbarrato et al., GCN 45979; Barthelmy et al., GCN 45985;
Ridnaia et al., GCN 45990) with the SAO RAS 0.5-m AS-500 (2)
telescope on 2026-10-18T00:50:15--2026-10-18T02:31:59.
We did not detect the OT possibly discovered by Swift/UVOT
(Kuin et al., GCN 45988) or any source within the XRT enhanced error
circle (Beardmore et al., GCN 45977) in our stacked image
down to the following limiting magnitude.
Date UT start t-T0 Exp, Filter UL
(mid, d) (n*s)
2026-10-18 00:50:15 0.4000 88*60 R 21.2
Our non-detection is in a good agreement with the other observations:
Fu et al., GCN 45978; Hagio et al., GCN 45980; Tan et al., GCN 45982;
Bao et al., GCN 45987; de Ugarte Postigo et al., GCN 45995).
This preliminary photometry (Vega) is based on nearby SDSS stars
(Lupton 2005 transformation) and not corrected for Galactic extinction.