TITLE: GCN CIRCULAR NUMBER: 40848 SUBJECT: GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations DATE: 25/06/27 11:55:09 GMT FROM: Nicolai Pankov at HSE, IKI RAS colinsergesen@gmail.com

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

We observed the field of GRB 250625A (Fermi GBM Team, GCN 40824; Ferro et al., GCN 40825; Beardmore et al., GCN 40827; Dichiara et al., GCN 40835; Di Lalla et al., GCN 40836) using the 0.7-meter AS-32 telescope of Abastumani Observatory (AbAO) and the 0.5-meter RC-500 telescope of INASAN Kislovodsk Observatory. The observations at AbAO started on 2025-06-25 at 17:41:35 UT and consisted of 71*60 sec exposures. The observations at RC-500 were carried out between 2025-06-25 18:19:40 UT and 2025-06-26 00:09:04 UT using 120 sec exposures. We do not detect the optical afterglow reported/followed by (Moskvitin et al., GCN 40828, Xin et al., GCN 40830; Malesani et al., GCN 40831; Lipunov et al., GCN 40826/40832; Zhu et al., GCN 40834, Fortin et al., GCN 40837; Adami et. al, GCN 40838; Brosio et. al, GCN 40839; Breeveld & Ferro, GCN 40840; WU et. al, GCN 40842; Ruocco et. al, GCN 40843; de Ugarte Postigo et. al, GCN 40846) in the R-band co-add images. The preliminary photometry is as follows:

Date UT start t-T0 Exp. Filter OT Err. UL Telescope (mid, days) (n*s) (3sigma) 2025-06-25 17:41:35 0.09176 71*60 R n/d n/d 20.0 AS-32 2025-06-25 18:38:08 0.14735 59*120 R n/d n/d 21.5 RC-500

The photometry has calibrated using stars from USNO-B1.0 (see Moskvitin et al., GCN 40828) and has not corrected for the Galactic extinction.

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