TITLE: GCN CIRCULAR NUMBER: 40001 SUBJECT: GRB 250328A: AbAO AS-32 Optical Observations DATE: 25/04/01 13:02:02 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 250328A (Brunet et. al, GCN 39910; Osborne et. al, GCN 39967) with the 0.7-meter AS-32 telescope of the Abastumani Astrophysical Observatory (AbAO). The observations started on (UT) 2025-03-28 20:21:40, i.e. about 0.17 days since trigger. The series of frames in the R-filter was obtained. We marginally detect the optical afterglow (Schneider et. al, GCN 39919; Schneider et. al, GCN 39920; Li et. al, GCN 39923; Li et. al, GCN 39936; Kumar et. al, GCN 39946; Klingler et. al, GCN 39968) in the stacked image. The preliminary photometry is as follows:

Date UT start t-T0 Exp. Filter OT Err UL (mid, days) (s) (3sigma) 2025-03-28 20:21:40 0.17064 82*60 R 22.2 S/N=1.7 21.6

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

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