TITLE: GCN CIRCULAR NUMBER: 44832 SUBJECT: GRB 260604C: Jinshan optical observations DATE: 26/06/05 02:52:57 GMT FROM: Zipei Zhu at NAOC <zpzhu@nao.cas.cn> Z.P. Zhu, X. Liu, D. Xu, J. An,S.Q. Jiang, L.B. He (NAOC), S.Y. Fu, A.D. Zhu, L. Lei (HUST), J.Z. Liu (XAO) report: We observed the field of GRB260604C detected by Fermi-GBM (Fermi GBM team, GCN 44822) and SVOM (Gotz et al, GCN 44823), using the JinShan 100B telescope located at Altay, Xinjiang, China. Observation started at 2026-06-04T20:32:14 UT, i.e., about 13 min post-burst, and a series of r-band frames were obtained. The previously reported optical counterpart (Lipunov et al, GCN 44827; Konno et al, GCN 44828) is detected in our first single frame with a brightness of R = 16.1 +/- 0.1, calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction. We acknowledge the excellent support from T.Q. Chen, and J.F. Zhang for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44832. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...