TITLE: GCN CIRCULAR NUMBER: 30709 SUBJECT: Swift GRB 210824A: Global MASTER-Net observations report DATE: 21/08/25 04:10:10 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 210824A ( K. L. Page et al., GCN 30700) errorbox 45612 sec after notice time and 45332 sec after trigger time at 2021-08-24 16:50:54 UT, with upper limit up to 19.4 mag. Observations started at twilight. The observations began at zenith distance = 46 deg. The sun altitude is -7.8 deg. MASTER-Tavrida robotic telescope located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the Swift GRB 210824A errorbox 48172 sec after notice time and 47892 sec after trigger time at 2021-08-24 17:33:34 UT, with upper limit up to 19.1 mag. Observations started at twilight. The observations began at zenith distance = 47 deg. The sun altitude is -10.9 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB 210824A errorbox 50320 sec after notice time and 50041 sec after trigger time at 2021-08-24 18:09:23 UT, with upper limit up to 17.4 mag. The observations began at zenith distance = 56 deg. The sun altitude is -21.7 deg. The galactic latitude b = 49 deg., longitude l = 17 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1698433 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 45363 | MASTER-SAAO | C | 60 | 16.0 | 45522 | MASTER-SAAO | C | 60 | 17.0 | 45602 | MASTER-SAAO | C | 60 | 17.2 | 46324 | MASTER-SAAO | C | 60 | 18.5 | 46483 | MASTER-SAAO | C | 60 | 18.7 | 46563 | MASTER-SAAO | C | 60 | 18.8 | 47281 | MASTER-SAAO | C | 60 | 19.4 | 47440 | MASTER-SAAO | C | 60 | 19.3 | 47520 | MASTER-SAAO | C | 60 | 19.4 | 47983 | MASTER-Tavrida | C | 180 | 17.8 | 49103 | MASTER-Tavrida | C | 180 | 19.1 | 49875 | MASTER-Tavrida | C | 60 | 18.7 | 50071 | MASTER-Kislovodsk | C | 60 | 15.8 | 50252 | MASTER-Tavrida | C | 180 | 19.0 | 50310 | MASTER-Kislovodsk | C | 180 | 15.1 | 50310 | MASTER-Kislovodsk | C | 180 | 15.3 | 51024 | MASTER-Tavrida | C | 60 | 18.4 | 51479 | MASTER-Tavrida | C | 60 | 18.4 | 51558 | MASTER-Tavrida | C | 60 | 18.4 | 52080 | MASTER-Kislovodsk | C | 60 | 16.6 | 52268 | MASTER-SAAO | C | 60 | 18.8 | 52527 | MASTER-Tavrida | C | 60 | 18.1 | 52605 | MASTER-Tavrida | C | 60 | 18.1 | 53102 | MASTER-Kislovodsk | C | 180 | 17.1 | 53102 | MASTER-Kislovodsk | C | 180 | 17.4 | 53227 | MASTER-SAAO | C | 60 | 18.6 | 53242 | MASTER-Kislovodsk | C | 60 | 17.0 | 53476 | MASTER-Tavrida | C | 60 | 17.9 | 53555 | MASTER-Tavrida | C | 60 | 17.9 | 54344 | MASTER-Kislovodsk | C | 180 | 17.0 | 54344 | MASTER-Kislovodsk | C | 180 | 17.1 | 54478 | MASTER-Tavrida | C | 180 | 18.0 | 54482 | MASTER-SAAO | C | 180 | 18.5 | 54617 | MASTER-Tavrida | C | 60 | 17.6 | 55565 | MASTER-SAAO | C | 180 | 17.0 | 55613 | MASTER-Tavrida | C | 180 | 17.8 | 55831 | MASTER-Tavrida | C | 60 | 17.5 | 56489 | MASTER-Kislovodsk | C | 60 | 12.8 | 56489 | MASTER-Kislovodsk | C | 60 | 14.0 | 56723 | MASTER-SAAO | C | 180 | 15.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.