GCN Circular 40965
X. Liu, J. An, Z.P. Zhu, S.Q. Jiang, L.B. He, D. Xu (NAOC), S.Y. Fu (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of EP250704a detected by EP/WXT (Li et al., GCN 40941), also likely by SVOM/GRM as GRB 250704B (Wang et al., GCN 40940), using the 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 18:01:00 UT on 2025-07-04, i.e., 9.74 hr after the trigger, and 12 x 300 s frames in Sloan i-band were obtained at a mid-time of 10.29 hr post-trigger.
The optical afterglow (e.g., Schneider at el., GCN 40942; Malesani at el., GCN 40945; Brivio at el., GCN 40947, etc.) was clearly detected in our stacked image, with a preliminary magnitude of i ~ 19.9, calibrated with nearby Pan-STARRS stars and without the Galactic extinction correction.
We acknowledge the excellent support from T.Q. Chen and J.L. He for enabling these observations.