TITLE:   GCN CIRCULAR
NUMBER:  45650
SUBJECT: EP260920a: LCO optical counterpart candidate
DATE:    26/09/20 02:33:40 GMT
FROM:    liuxing@nao.cas.cn


X. Liu, D. Xu, J. An, Z. Fan, J.F. Gou, L.B. He, Y.L. Hua, S.Q. Jiang, W.X. Li, R.D. Liang, Q. Zhao, Z.P. Zhu (NAOC), Y.L. Hua (PMO), S.Y. Fu, L. Lei (HUST) report:

We observed the field of EP260920a triggered by Einstein Probe (EP; Ni et al., GCN 45649), using an LCO 1m telescope network. We obtained 3 x 200 s exposures in the w filter.

A residual optical transient (OT) is detected at coordinates

R.A. (J2000) = 01:46:06.71
Dec. (J2000) = -13:59:06.1 

after subtracting the archival Legacy Survey image, which is within the EP-FXT error circle (EP; Ni et al., GCN 45649). There is a known source at the above coordinates, which has g = 23.39, r = 22.02, i = 20.68, and z = 20.14, and is classified as Point-like in Legacy Survey. The OT and the known source together has r ~ 21.67 mag in the LCO stacked image at a median time of ~1.174 hr post-trigger, and the OT was decaying in the LCO three images.

We thus think the above OT/known source could be optical counterpart of EP260920a.