//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29926 SUBJECT: Swift GRB210502.74: Global MASTER-Net observations report DATE: 21/05/03 06:40:14 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB210502.74 (trigger No 1046414,18h 02m 58.08s , -29d 49m 04.8s, R=0.05) errorbox 45466 sec after notice time and 45874 sec after trigger time at 2021-05-03 06:24:07 UT, with upper limit up to 16.5 mag. The observations began at zenith distance = 19 deg. The sun altitude is -60.1 deg. The galactic latitude b = -4 deg., longitude l = 1 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1605655 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 45964 | MASTER-OAFA | C | 180 | 16.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.