TITLE:   GCN CIRCULAR
NUMBER:  46015
SUBJECT: EP261023a: NOT optical counterpart candidate
DATE:    26/10/23 15:42:14 GMT
FROM:    syfu@nao.cas.cn

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

We observed the field of EP261023a detected by EP (Yang et al., GCN 46014), using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 5 x 200 s Sloan r-band frames. 

An optical source is detected within the EP-FXT error circle (Yang et al., GCN 46014) in the stacked image at coordinates

R.A. (J2000) = 0:15:56.16
Dec. (J2000) = +51:35:54.81

with an uncertainty of ~ 0.4 arcsec. The source had r = 22.71+/-0.13 mag at a median time of ~ 63.7 min post-trigger, calibrated with Pan-STARRS DR2 and not corrected for Galactic extinction.

An object is weakly detected at the above position in the Pan-STARRS survey images, and it has r = 23.3 +/- 0.2, i = 21.3 +/- 0.2, and z = 20.4 +/- 0.1 mag, calibrated with Pan-STARRS field stars. If the object is interpreted as the host galaxy, it is consistent with an early-type galaxy.

We think the NOT source is the optical counterpart candidate of EP261023a.