TITLE: GCN CIRCULAR NUMBER: 30176 SUBJECT: Swift GRB 210610B: Global MASTER-Net observations report DATE: 21/06/10 21:15:40 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) was pointed to the Swift GRB 210610B ( K. L. Page et al., GCN 30170) errorbox 145 sec after trigger time at 2021-06-10 19:53:52 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 30 deg. The sun altitude is -21.6 deg. MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 210610B errorbox 0 sec after notice time and 582 sec after trigger time at 2021-06-10 20:01:10 UT, with upper limit up to 19.2 mag. The observations began at zenith distance = 52 deg. The sun altitude is -54.2 deg. MASTER-Tavrida robotic telescope located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the Swift GRB 210610B errorbox 15 sec after notice time and 598 sec after trigger time at 2021-06-10 20:01:25 UT, with upper limit up to 20.3 mag. The observations began at zenith distance = 31 deg. The sun altitude is -19.1 deg. MASTER-IAC robotic telescope located in Spain (IAC Teide Observatory) was pointed to the Swift GRB 210610B errorbox 3486 sec after notice time and 4069 sec after trigger time at 2021-06-10 20:59:16 UT, with upper limit up to 17.6 mag. Observations started at twilight. The observations began at zenith distance = 44 deg. The sun altitude is -12.3 deg. The galactic latitude b = 40 deg., longitude l = 29 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1633397 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 160 | MASTER-Kislovodsk | C | 30 | 17.5 | 215 | MASTER-Kislovodsk | C | 40 | 17.7 | 643 | MASTER-SAAO | P\ | 120 | 18.3 | 798 | MASTER-SAAO | P\ | 430 | 19.0 | Coadd 658 | MASTER-Tavrida | C | 120 | 19.1 | 838 | MASTER-Tavrida | C | 480 | 20.0 | Coadd 658 | MASTER-Tavrida | C | 120 | 19.1 | 722 | MASTER-Kislovodsk | C | 130 | 18.2 | 722 | MASTER-Kislovodsk | P| | 130 | 18.3 | 792 | MASTER-SAAO | P\ | 140 | 18.4 | 813 | MASTER-Tavrida | C | 150 | 19.2 | 813 | MASTER-Tavrida | C | 150 | 19.1 | 967 | MASTER-SAAO | P\ | 170 | 18.5 | 997 | MASTER-Tavrida | C | 180 | 19.2 | 997 | MASTER-Tavrida | C | 180 | 19.1 | 1161 | MASTER-SAAO | P\ | 180 | 18.5 | 1341 | MASTER-SAAO | P\ | 540 | 19.1 | Coadd 1197 | MASTER-Tavrida | C | 180 | 19.4 | 1359 | MASTER-Kislovodsk | C | 180 | 13.7 | 1359 | MASTER-Kislovodsk | P| | 180 | 18.5 | 1361 | MASTER-SAAO | P\ | 180 | 18.6 | 1403 | MASTER-Tavrida | C | 180 | 19.5 | 1403 | MASTER-Tavrida | C | 180 | 19.1 | 1560 | MASTER-SAAO | P\ | 180 | 18.5 | 1603 | MASTER-Tavrida | C | 180 | 19.5 | 1603 | MASTER-Tavrida | C | 180 | 19.3 | 1760 | MASTER-SAAO | P\ | 180 | 18.6 | 1940 | MASTER-SAAO | P\ | 540 | 19.2 | Coadd 1802 | MASTER-Tavrida | C | 180 | 19.4 | 1802 | MASTER-Tavrida | C | 180 | 19.1 | 1959 | MASTER-SAAO | P\ | 180 | 18.7 | 2001 | MASTER-Tavrida | C | 180 | 19.5 | 2181 | MASTER-Tavrida | C | 540 | 20.2 | Coadd 2001 | MASTER-Tavrida | C | 180 | 19.1 | 2019 | MASTER-Kislovodsk | C | 180 | 18.2 | 2019 | MASTER-Kislovodsk | P| | 180 | 18.9 | 2159 | MASTER-SAAO | P\ | 180 | 18.5 | 2201 | MASTER-Tavrida | C | 180 | 19.5 | 2201 | MASTER-Tavrida | C | 180 | 19.3 | 2358 | MASTER-SAAO | P\ | 180 | 18.6 | 2401 | MASTER-Tavrida | C | 180 | 19.6 | 2401 | MASTER-Tavrida | C | 180 | 19.4 | 2558 | MASTER-SAAO | P\ | 180 | 16.5 | 2600 | MASTER-Tavrida | C | 180 | 19.6 | 2780 | MASTER-Tavrida | C | 540 | 20.3 | Coadd 2600 | MASTER-Tavrida | C | 180 | 19.3 | 2743 | MASTER-Kislovodsk | C | 180 | 13.8 | 2743 | MASTER-Kislovodsk | P| | 180 | 18.9 | 2757 | MASTER-SAAO | P\ | 180 | 15.7 | 2800 | MASTER-Tavrida | C | 180 | 19.6 | 2800 | MASTER-Tavrida | C | 180 | 19.4 | 2957 | MASTER-SAAO | P\ | 180 | 17.3 | 2999 | MASTER-Tavrida | C | 180 | 19.7 | 2999 | MASTER-Tavrida | C | 180 | 19.4 | 3156 | MASTER-SAAO | P\ | 180 | 16.6 | 3199 | MASTER-Tavrida | C | 180 | 18.8 | 3379 | MASTER-Tavrida | C | 540 | 19.9 | Coadd 3199 | MASTER-Tavrida | C | 180 | 18.3 | 3356 | MASTER-SAAO | P\ | 180 | 17.2 | 3398 | MASTER-Tavrida | C | 180 | 19.6 | 3398 | MASTER-Tavrida | C | 180 | 18.9 | 3418 | MASTER-Kislovodsk | C | 180 | 18.3 | 3418 | MASTER-Kislovodsk | P| | 180 | 18.8 | 3555 | MASTER-SAAO | P\ | 180 | 17.0 | 3598 | MASTER-Tavrida | C | 180 | 19.6 | 3598 | MASTER-Tavrida | C | 180 | 19.2 | 3755 | MASTER-SAAO | P\ | 180 | 17.3 | 3797 | MASTER-Tavrida | C | 180 | 19.5 | 3797 | MASTER-Tavrida | C | 180 | 19.2 | 3954 | MASTER-SAAO | P\ | 180 | 15.7 | 3997 | MASTER-Tavrida | C | 180 | 19.8 | 3997 | MASTER-Tavrida | C | 180 | 19.4 | 4154 | MASTER-SAAO | P\ | 180 | 16.4 | 4099 | MASTER-IAC | C | 60 | 17.6 | 4099 | MASTER-IAC | C | 60 | 17.3 | 4239 | MASTER-IAC | I | 180 | 16.9 | 4239 | MASTER-IAC | R | 180 | 17.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.