TITLE: GCN CIRCULAR NUMBER: 30759 SUBJECT: Fermi GRB 210903A: Global MASTER-Net observations report DATE: 21/09/03 18:15:21 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) started inspect of the Fermi GRB 210903A ( Fermi GBM team, GCN 30752) errorbox 56033 sec after notice time and 56098 sec after trigger time at 2021-09-03 17:25:15 UT, with upper limit up to 18.6 mag. Observations started at twilight. The observations began at zenith distance = 69 deg. The sun altitude is -12.8 deg. The galactic latitude b = 74 deg., longitude l = 164 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1708312 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 56128 | 2021-09-03 17:25:15 | MASTER-Tavrida | (12h 02m 08.49s , +38d 59m 08.2s) | C | 60 | 17.6 | 56207 | 2021-09-03 17:26:34 | MASTER-Tavrida | (12h 12m 24.55s , +39d 00m 39.2s) | C | 60 | 17.8 | 56438 | 2021-09-03 17:30:25 | MASTER-Tavrida | (12h 12m 59.54s , +40d 55m 06.6s) | C | 60 | 18.1 | 56517 | 2021-09-03 17:31:44 | MASTER-Tavrida | (12h 03m 33.73s , +42d 46m 35.9s) | C | 60 | 18.0 | 57008 | 2021-09-03 17:39:55 | MASTER-Tavrida | (12h 14m 34.76s , +42d 47m 02.0s) | C | 60 | 18.3 | 57404 | 2021-09-03 17:46:31 | MASTER-Tavrida | (12h 02m 01.58s , +38d 58m 43.9s) | C | 60 | 18.5 | 57483 | 2021-09-03 17:47:50 | MASTER-Tavrida | (12h 12m 26.04s , +38d 59m 03.2s) | C | 60 | 18.6 | 57562 | 2021-09-03 17:49:09 | MASTER-Tavrida | (12h 02m 26.10s , +40d 54m 08.7s) | C | 60 | 18.5 | 57641 | 2021-09-03 17:50:28 | MASTER-Tavrida | (12h 13m 03.20s , +40d 52m 36.4s) | C | 60 | 18.5 | 57720 | 2021-09-03 17:51:47 | MASTER-Tavrida | (12h 03m 41.09s , +42d 47m 32.7s) | C | 60 | 18.5 | 58369 | 2021-09-03 18:02:36 | MASTER-Tavrida | (11h 53m 47.03s , +42d 45m 34.2s) | C | 60 | 18.3 | 58448 | 2021-09-03 18:03:55 | MASTER-Tavrida | (12h 14m 40.54s , +42d 46m 09.0s) | C | 60 | 18.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.