GCN 44152: EP260329a: NOT optical counterpart candidate

L.B. He, S.Q. Jiang, Z.P. Zhu, J. An, X. Liu, D. Xu (NAOC), S.Y. Fu (HUST), J. P. U. Fynbo (DAWN/NBI), K. Valeckas (NOT) report:

We observed the field of EP260329a detected by Einstein Probe (EP), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 3 x 300 s frames in the Sloan r-band.

An uncatalogued optical source is detected within the EP-WXT  error circle (Yang et al., GCN 44141) at coordinates

R.A. (J2000) = 5.4770 (deg)
Dec. (J2000) = 82.4894 (deg)

with an uncertainty of ~ 0.5 arcsec. The source has r ~ 21.6 mag (AB) at a median time of 45 mins after the EP trigger, calibrated with nearby PanSTARRS1-dr2 catalog and not corrected for Galactic extinction. No source is present at the above position in PanSTARRS down to a 5-sigma limit of r ~22.3 mag. No NEO object would be at the above position at the NOT observational time by checking MPC.

We thus think the source could be the optical counterpart of EP260329a.