TITLE: GCN CIRCULAR NUMBER: 30984 SUBJECT: GRB 211024B: Nanshan/NEXT optical afterglow detection DATE: 21/10/25 01:27:33 GMT FROM: Dong Xu at NAOC/CAS <dxu@nao.cas.cn> Z.P. Zhu (NAOC, HUST), S.Y. Fu, X. Liu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report: We observed the field of GRB 211024B (Gropp et al., GCN 30980) using the NEXT-0.6m optical telescope located at Nanshan, Xinjiang, China. Observations automatically started at 22:23:13 UT on 2021-10-24, i.e., 157 s after the BAT trigger. A series of 3x40 s, 3x60 s and 12x90 s frames in the Sloan r-filter were obtained. An uncatalogued evolving optical transient is detected within the Swift/BAT error circle (Gropp et al., GCN 30980), at coordinates R.A. = 10:18:51.12 Dec. = +24:34:05.16 with an uncertainty of 0.5 arcsec. The OT had r = 18.4 +/- 0.1 mag in our first image, brightened to a peak of r ~ 17.6 at ~ 378 s, and then faded with a powerlaw decay as F(t) ~ t^-0.94, all calibrated with nearby PS1 stars. We thus conclude that the OT is the optical afterglow of the burst.