TITLE:   GCN CIRCULAR
NUMBER:  39496
SUBJECT: EP250223a: CrAO ZTSH optical observation
DATE:    25/02/26 17:18:16 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>

 E. Mazaeva (IKI), V. Rumyantsev (CrAO), A. Pozanenko (IKI), N. Pankov
(HSE, IKI), A. Volnova (IKI) report on behalf of IKI GRB-FuN collaboration:

We observed the field of EP250223a (Lian et al., GCN 39429) 2.6-meter ZTSh
telescope of CrAO starting on (UT) 2025-02-25 18:01:15.

The optical counterpart of EP250223a (Hauptmann et al., GCN 39436; Wu et
al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441;
Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Ducoin
et al., GCN 39453; O’Neill et al., GCN 39455; Aryan et al., GCN 39464;
Saikia et al., GCN 39472; Wang et al., GCN 39476) at the redshift of 2.756
(Levan et al., GCN 39438) is clearly detected.
The preliminary photometry of the optical counterpart is the following:

Date UT start T-T0 Exp. Filter OT Err. UL(3sigma)
(mid, days) (s)

2025-02-25 18:01:15 2.15250 41x120 R 20.62 0.05 22.2

The magnitudes were calibrated using nearby PS1 stars using Lupton
transformations to R-magnitude. No correction has been made for a Galactic
extinction towards the counterpart.