TITLE: GCN CIRCULAR NUMBER: 29499 SUBJECT: GRB 210204A (ZTF21aagwbjr/AT2021buv): continued CrAO and AbAO optical observations DATE: 21/02/12 23:18:51 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), A. Pozanenko (IKI), V. Rumyantsev (CrAO), R. Ya. Inasaridze (AbAO), N. Pankov (HSE) report on behalf of GRB IKI FuN: We continued observation of the ZTF21aagwbjr/AT2021buv transient (Kool et al., GCN 29405) at the redshift of 0.876 (Xu et al., GCN 29432) which is an afterglow (Kennea et al., GCN 29413; Teja et al., GCN 29414; Belkin et al., GCNs 29417, 29438; Rossi et al., GCN 29433; Gupta et al., GCN 29490) of GRB 210204A (Fermi GBM team, GCN 29390; Li et al., GCN 29392; Hurley et al., GCN 29408; Waratkar et al., GCN 29410; Frederiks et al., GCN 29415). Images in R-filter were taken with AS-32 telescope of Abastumani observatory (AbAO) and ZTSh 2.6m telescope of CrAO observatory on 2021-02-09 and 2021-02-11. Preliminary photometry of the afterglow in combined images is following Date UT start t-T0 Filter Exp. OT Err. UL(3s) Telescope (mid, days) (s) 2021-02-09 18:41:28 5.52572 R 25*120 21.09 0.08 22.6 ZTSh 2021-02-09 19:28:42 5.55610 R 43*60 21.4 0.2 22.5 AS-32 2021-02-11 18:18:20 7.50966 R 50*60 21.8 0.2 22.5 AS-32 2021-02-11 21:32:47 7.64817 R 30*120 21.6 0.3 21.8 ZTSh The photometry is based on the nearby USNO-B1.0 stars USNO-B1.0_id R2 1014-0149033 15.43 1014-0149115 17.00 A light curve can be found in http://grb.rssi.ru/GRB210204A/GRB210204A_lc.png Our photometry confirms suggested jet-break (Rossi et al. GCN 29433; Gupta et al., GCN 29490).