TITLE: GCN CIRCULAR NUMBER: 30762 SUBJECT: Swift GRB210903.59: Global MASTER-Net observations report DATE: 21/09/04 14:06:08 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> 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-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the Swift GRB210903.59 (trigger No 1071768,19h 58m 08.69s , +34d 58m 31.8s, R=0.0013) errorbox 10573 sec after notice time and 10763 sec after trigger time at 2021-09-03 17:06:18 UT, with upper limit up to 18.4 mag. Observations started at twilight. The observations began at zenith distance = 21 deg. The sun altitude is -9.6 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB210903.59 errorbox 17837 sec after notice time and 18026 sec after trigger time at 2021-09-03 19:07:21 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 13 deg. The sun altitude is -32.4 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB210903.59 errorbox 34110 sec after notice time and 34300 sec after trigger time at 2021-09-03 23:38:35 UT, with upper limit up to 16.6 mag. The observations began at zenith distance = 72 deg. The sun altitude is -17.6 deg. The galactic latitude b = 3 deg., longitude l = 71 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1708701 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 10854 | MASTER-Tavrida | C | 180 | 16.0 | 11468 | MASTER-Tavrida | C | 180 | 17.4 | 12664 | MASTER-Tavrida | C | 180 | 17.9 | 14017 | MASTER-Tavrida | C | 180 | 18.0 | 14475 | MASTER-Tavrida | C | 180 | 18.2 | 16334 | MASTER-Tavrida | C | 180 | 16.6 | 18117 | MASTER-Kislovodsk | C | 180 | 16.8 | 18117 | MASTER-Kislovodsk | C | 180 | 17.0 | 18263 | MASTER-Tavrida | C | 180 | 18.2 | 20001 | MASTER-Kislovodsk | C | 180 | 18.0 | 20001 | MASTER-Kislovodsk | C | 180 | 17.7 | 20140 | MASTER-Tavrida | C | 180 | 18.4 | 21805 | MASTER-Kislovodsk | C | 180 | 17.7 | 21805 | MASTER-Kislovodsk | C | 180 | 18.0 | 22143 | MASTER-Tavrida | C | 180 | 17.1 | 23689 | MASTER-Kislovodsk | C | 180 | 17.5 | 23689 | MASTER-Kislovodsk | C | 180 | 17.8 | 24010 | MASTER-Tavrida | C | 180 | 18.2 | 25493 | MASTER-Kislovodsk | C | 180 | 17.2 | 25494 | MASTER-Kislovodsk | C | 180 | 17.6 | 25959 | MASTER-Tavrida | C | 180 | 18.2 | 27299 | MASTER-Kislovodsk | C | 180 | 16.6 | 27299 | MASTER-Kislovodsk | C | 180 | 17.4 | 27952 | MASTER-Tavrida | C | 180 | 18.1 | 29103 | MASTER-Kislovodsk | C | 180 | 16.0 | 29103 | MASTER-Kislovodsk | C | 180 | 17.0 | 29947 | MASTER-Tavrida | C | 180 | 18.1 | 31940 | MASTER-Tavrida | C | 180 | 18.2 | 33748 | MASTER-Tavrida | C | 180 | 17.8 | 34390 | MASTER-OAFA | C | 180 | 16.0 | 35611 | MASTER-Tavrida | C | 180 | 17.6 | 36466 | MASTER-OAFA | C | 180 | 16.5 | 37511 | MASTER-Tavrida | C | 180 | 17.9 | 37844 | MASTER-Kislovodsk | C | 180 | 12.6 | 38341 | MASTER-OAFA | C | 180 | 16.6 | 39331 | MASTER-Tavrida | C | 180 | 17.2 | 40219 | MASTER-OAFA | C | 180 | 16.6 | 41730 | MASTER-Tavrida | C | 180 | 17.2 | 42215 | MASTER-OAFA | C | 180 | 16.4 | 51950 | MASTER-OAFA | C | 180 | 15.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.