TITLE: GCN CIRCULAR NUMBER: 39539 SUBJECT: GRB 250226A: AbAO AS-32 Optical Upper Limit DATE: 25/02/28 20:42:33 GMT FROM: Nicolai Pankov at HSE, IKI RAS colinsergesen@gmail.com

N. Pankov (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:

We performed optical observations of the field of GRB 250226A (The Fermi GBM team, GCN 39479; V.Lipunov et. al, GCN 39481; Jiang et. al, GCN 39482; An et. al, GCN 39486; Zhu et. al, GCN 39487; Magnani et. al, GCN 39488; Li et. al, GCN 39489; Li et. al, GCN 39492; Aryan et. al, GCN 39509; Zou et. al, GCN 39511; Jiang et. al, GCN 39513; Li et. al, GCN 39514; Junjie-Jin et. al, GCN 39515; Thakur et. al, GCN 39518; Poidevin et. al, GCN 39524; Pathak et. al, GCN 39530) in the R filter with the 0.7-meter AS-32 telescope of the Abastumani Astrophysical Observatory. The observations started on (UT) 2025-02-28 00:25:49, i.e. ~1.76 days since trigger and consists of 70*60 sec exposures. We do not detect the optical counterpart in the stacked image. The preliminary upper limit is as follows:

Date UT start t-T0 Exp. Filter UL(3sigma) (mid, days) (s) 2025-02-28 00:25:49 1.76796 70*60 R 21.4

The photometry is based on nearby stars from the USNO-B1.0 catalog and has not been corrected for the Galactic extinction.

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