TITLE: GCN CIRCULAR NUMBER: 29766 SUBJECT: Integral GRB210406.72: Global MASTER-Net observations report DATE: 21/04/06 17:19:07 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Integral GRB210406.72 (trigger No 9126,08h 49m 46.12s , +76d 30m 59.0s, R=0.0516667) errorbox 10 sec after notice time and 28 sec after trigger time at 2021-04-06 17:11:57 UT, with upper limit up to 17.0 mag. Observations started at twilight. The observations began at zenith distance = 34 deg. The sun altitude is -16.3 deg. The galactic latitude b = 33 deg., longitude l = 137 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1585485 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 33 | MASTER-Kislovodsk | P- | 10 | 14.6 | 52 | MASTER-Kislovodsk | P- | 10 | 14.5 | 70 | MASTER-Kislovodsk | P- | 10 | 14.6 | 92 | MASTER-Kislovodsk | P- | 20 | 16.7 | 120 | MASTER-Kislovodsk | P- | 20 | 16.6 | 153 | MASTER-Kislovodsk | P- | 30 | 16.8 | 191 | MASTER-Kislovodsk | P- | 30 | 17.0 | The observation and reduction will continue. The message may be cited.