GCN Circular 38906
Subject
EP250111a: NOT likely optical counterpart
Date
2025-01-11T09:42:34Z (3 days ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Y. Fu, J. An, S.Q. Jiang, X. Liu, Z.P. Zhu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), A. H. de la Fuente, S. G. Sorensen (NOT) report on behalf of a large collaboration:
We observed the field of EP250111a detected by Einstein Probe (EP, Zhao et al., GCN 38905), using the ALFOSC instrument mounted on the Nordic Optical Telescope (NOT). Observations started at 02:58:45.5 UT on 2025-01-11, i.e. 1.63 hr after the trigger, and 9 x100 s frames were obtained in the SDSS-r band.
An uncatalogued source is detected in the stacked frame within the EP/FXT error circle (EP, Zhao et al., GCN 38905) and localized at coordinates
R.A. (J2000) = 06:28:43.29
Dec. (J2000) = +56:53:54.76
with an uncertainty of ~ 0.5 arcsec. The source has r ~ 20.7 mag, calibrated with Pan-STARRS DR1 and not corrected for Galactic extinction. There was no known NEO object at the above position by checking MPC.
We thus conclude the source is very likely the optical counterpart of EP250111a.
Further observations are encouraged.