TITLE: GCN CIRCULAR NUMBER: 29924 SUBJECT: MAXI GRB210501.83: Global MASTER-Net observations report DATE: 21/05/02 08:51:09 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) started inspect of the MAXI GRB210501.83 (trigger No 335675984,18h 03m 41.52s , -29d 48m 14.4s, R=1) errorbox 113 sec after notice time and 12664 sec after trigger time at 2021-05-01 23:21:29 UT, with upper limit up to 15.9 mag. The observations began at zenith distance = 75 deg. The sun altitude is -24.1 deg. The galactic latitude b = -4 deg., longitude l = 2 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1605264 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 12754 | 2021-05-01 23:21:29 | MASTER-Kislovodsk | (18h 02m 22.24s , -30d 00m 55.3s) | P| | 180 | 15.9 | The observation and reduction will continue. The message may be cited.