TITLE: GCN CIRCULAR NUMBER: 30260 SUBJECT: Swift GRB210619.99: Global MASTER-Net observations report DATE: 21/06/20 00:10:13 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), 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 GRB210619.99 (trigger No 1056757,21h 18m 51.12s , +33d 51m 36.0s, R=0.05) errorbox 0 sec after notice time and 36 sec after trigger time at 2021-06-20 00:00:02 UT, with upper limit up to 16.7 mag. The observations began at zenith distance = 72 deg. The sun altitude is -70.4 deg. The galactic latitude b = -11 deg., longitude l = 81 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1640637 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 42 | MASTER-SAAO | P\ | 10 | 15.8 | 57 | MASTER-SAAO | P\ | 40 | 16.5 | Coadd 71 | MASTER-SAAO | P\ | 10 | 15.6 | 106 | MASTER-SAAO | P\ | 20 | 16.2 | 150 | MASTER-SAAO | P\ | 30 | 16.5 | 205 | MASTER-SAAO | P\ | 40 | 16.4 | 269 | MASTER-SAAO | P\ | 50 | 16.7 | 344 | MASTER-SAAO | P\ | 60 | 16.7 | The observation and reduction will continue. The message may be cited.