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, H.Z. Wu, 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.