TITLE:   GCN CIRCULAR
NUMBER:  42922
SUBJECT: EP251130a: Mondy optical observations
DATE:    25/12/01 15:00:28 GMT
FROM:    Alina Volnova at IKI RAS <alinusss@gmail.com>

A. A. Volnova (IKI), A. S. Pozanenko (IKI), E. Klunko (ISTP), N. S. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN:

We observed the field of the X-ray transient EP251130a (Wu et al., GCN 42903; Zhang et al., GCN 42915), also detected by Swift/XRT (Evans et al., GCN 42908) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) starting on 2025-11-30 (UT) 15:06:18 in R filter. The optical counterpart (Dornic et al., GCN 42904; He et al. GCN 42914; Gupta et al. GCN 42916; Zheng et al. GCN 42917; van Dalen et al., GCN 42918; Moskvitin and Spiridonova, GCN 42919; Aryan et al., GCN 42921) is detected in the stacked frame. Preliminary photometry is the following:

Date        UT start  t-T0       Exp.    Filter  OT     Err.  UL      Site/Instrum
                     (mid,days)  (n*s)                       (3sigma)
2025-11-30  15:06:18  0.18716    60*120  R       21.76  0.20  22.1    Mondy/AZT-33IK

The photometry is calibrated using USNO-B1.0 stars from Moskvitin and Spiridonova, GCN 42919, and is not corrected for the Galactic extinction.