TITLE:   GCN CIRCULAR
NUMBER:  36774
SUBJECT: EP240626a: Montarrenti Observatory optical upper limit
DATE:    24/06/27 22:11:13 GMT
FROM:    Simone Leonini at Montarrenti Observatory (Siena, Italy) <s.leonini@iol.it>

S. Leonini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy), K. Kalinowski (Aarhus University, Department of Physics and Astronomy) and B. De Simone (Universita' degli Studi Di Salerno) report:

we observed the field of the possible optical countepart of the X-ray transient EP240626a (Einstein Probe, GCN 36766, Wu et al.; GCN 36767, Perez-Garcia et al.; GCN 36773, Zheng et al.)  with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88).

The observations were started at 2024-06-26 21:22:28 UT (approximately 15 hours after the discovery of the X-ray transient) stacking 24x40s Rc-band CCD images.
 
We have not found any optical transient candidate within the error-box of the EP mission position with the following upper limit: 

MJD           Filter   Limit      
60488.3964    Rc      > 19.40    

Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied.