TITLE: GCN CIRCULAR NUMBER: 26536 SUBJECT: Swift GRB 191221B: Global MASTER-Net observations report DATE: 19/12/21 21:27:29 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov, D. Cheryasov (Lomonosov Moscow State University, SAI, Physics Department), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA), H.Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 191221B ( S Laha et al., GCN 26534) errorbox 1677 sec after notice time and 1700 sec after trigger time at 2019-12-21 21:07:33 UT, with upper limit up to 17.0 mag. The observations began at zenith distance = 69 deg. The sun altitude is -30.6 deg. The galactic latitude b = 16 deg., longitude l = 273 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1234924 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 1790 | MASTER-SAAO | P\ | 180 | 16.0 | 1991 | MASTER-SAAO | P\ | 180 | 16.7 | 2192 | MASTER-SAAO | P\ | 180 | 16.6 | 2394 | MASTER-SAAO | P\ | 180 | 17.0 | The observation and reduction will continue. The message may be cited.