TITLE: GCN CIRCULAR NUMBER: 30249 SUBJECT: Swift GRB210618.07: Global MASTER-Net observations report DATE: 21/06/18 01:54:19 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-IAC robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Spain (IAC Teide Observatory) was pointed to the Swift GRB210618.07 (trigger No 1056426,15h 43m 16.80s , +46d 02m 34.8s, R=0.05) errorbox 14 sec after notice time and 41 sec after trigger time at 2021-06-18 01:44:18 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 37 deg. The sun altitude is -37.7 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB210618.07 errorbox 28 sec after notice time and 56 sec after trigger time at 2021-06-18 01:44:33 UT, with upper limit up to 17.5 mag. The observations began at zenith distance = 77 deg. The sun altitude is -51.4 deg. The galactic latitude b = 51 deg., longitude l = 73 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1639424 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 47 | MASTER-IAC | P| | 10 | 16.6 | 61 | MASTER-OAFA | C | 10 | 16.5 | 76 | MASTER-OAFA | C | 40 | 17.4 | Coadd 67 | MASTER-IAC | P| | 10 | 16.6 | 92 | MASTER-IAC | P| | 20 | 17.3 | 91 | MASTER-OAFA | C | 10 | 16.6 | 122 | MASTER-IAC | P| | 20 | 17.3 | 133 | MASTER-OAFA | C | 20 | 17.0 | 159 | MASTER-IAC | P| | 30 | 17.6 | 178 | MASTER-OAFA | C | 30 | 17.3 | 205 | MASTER-IAC | P| | 40 | 18.0 | 233 | MASTER-OAFA | C | 40 | 17.4 | 260 | MASTER-IAC | P| | 50 | 18.2 | 297 | MASTER-OAFA | C | 50 | 17.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.