TITLE:   GCN CIRCULAR
NUMBER:  43959
SUBJECT: EP260306a: Mondy optical upper limit
DATE:    26/03/11 10:31:25 GMT
FROM:    Alina Volnova at IKI RAS <alinusss@gmail.com>


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

We observed the field of the fast X-ray transient EP260306a (Huang et al., GCNs 43930, 43937) using the AZT-33IK 1.5m telescope of the Mondy observatory on March 7, 8, and 9 taking several 120-seconds frames in the R band. In the stacked frame of the three epochs we do not detect the optical counterpart reported previously (Li et al., GCN 43929; Globus et al., GCN 43931; Ma et al., GCN 43933; Levan et al., GCN 43934). 
Preliminary photometry of the galaxy and observational details are the following:

Date        UT start  t-T0      Exp.    Filter Obj.   Err.  UL      Site/Telescope
                     (mid,days) (n*s)                      (3sigma)
2026-03-07  15:44:24  1.61672   33*120  R      n/d    n/d   22.8    Mondy/AZT-33IK
2026-03-08  14:30:42  2.57040   40*120  R      n/d    n/d   22.1    Mondy/AZT-33IK
2026-03-09  16:24:33  3.64947   40*120  R      n/d    n/d   23.2    Mondy/AZT-33IK

The photometry is based on nearby USNO-B1.0 stars (R2-magnitudes) and is not corrected for Galactic extinction.