{
  "body": "A. A. Volnova (IKI), V. V. Rumyantsev (CrAO), A. S. Pozanenko (IKI), N. S. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN:\n\nWe observed the field of the fast X-ray transient EP251220a detected by EP/WXT (Liu et al., GCN 43162) with the ZTSh 2.6m telescope of CrAO taking several 120-second frames in R-band. The observations started on Dec. 22 at UT 20:32:36, i.e., ~ 2.5 days after the EP/WXT trigger. In the stacked image we detect the optical counterpart reported previously (Sánchez Álvarez et al., GCN 43167; Kumar et al., GCN 43169; Rakotondrainibe  et al., GCN 43170; Busmann et al., GCN 43181; van Hoof et al., GCN 43182; An et al., GCN 43184; Passaleva et al., GCN 43185). Preliminary photometry and observational details are the following:\n\nDate        UT start  t-T0       Exp.    Filter Obj.   Err.   UL       Site/Telescope\n                     (mid,days)  (n*s)                       (3sigma)\n2025-12-22  20:32:36  2.51642    17*120  R      22.55  0.20   22.9     CrAO/ZTSh\n\nThe photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction.",
  "subject": "EP251220a: CrAO ZTSh optical observations",
  "circularId": 43221,
  "submittedHow": "web",
  "eventId": "EP251220a",
  "bibcode": "2025GCN.43221....1V",
  "createdOn": 1766513955451,
  "submitter": "Alina Volnova at IKI RAS <alinusss@gmail.com>",
  "format": "text/plain"
}