TITLE: GCN CIRCULAR NUMBER: 30049 SUBJECT: Fermi GRB 210518A: Global MASTER-Net observations report DATE: 21/05/18 19:41:21 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-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 210518A ( Fermi GBM team, GCN 30045) errorbox 21119 sec after notice time and 21211 sec after trigger time at 2021-05-18 18:57:41 UT, with upper limit up to 17.5 mag. Observations started at twilight. The observations began at zenith distance = 48 deg. The sun altitude is -16.4 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 210518A errorbox 22517 sec after notice time and 22609 sec after trigger time at 2021-05-18 19:20:59 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 44 deg. The sun altitude is -22.7 deg. The galactic latitude b = 28 deg., longitude l = 77 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1615984 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21242 | 2021-05-18 18:57:41 | MASTER-Tavrida | (17h 48m 41.51s , +49d 49m 53.4s) | C | 60 | 14.3 | 21321 | 2021-05-18 18:59:00 | MASTER-Tavrida | (17h 44m 23.63s , +51d 42m 07.4s) | C | 60 | 17.0 | 21401 | 2021-05-18 19:00:20 | MASTER-Tavrida | (17h 57m 38.57s , +51d 41m 50.7s) | C | 60 | 17.5 | 21482 | 2021-05-18 19:01:41 | MASTER-Tavrida | (17h 59m 42.95s , +45d 59m 33.9s) | C | 60 | 17.1 | 22181 | 2021-05-18 19:13:20 | MASTER-Tavrida | (17h 42m 50.03s , +47d 56m 08.8s) | C | 60 | 16.6 | 22260 | 2021-05-18 19:14:40 | MASTER-Tavrida | (18h 01m 23.46s , +49d 48m 32.6s) | C | 60 | 16.0 | 22340 | 2021-05-18 19:15:59 | MASTER-Tavrida | (17h 53m 46.00s , +47d 53m 44.4s) | C | 60 | 15.3 | 22419 | 2021-05-18 19:17:19 | MASTER-Tavrida | (18h 05m 59.67s , +47d 53m 29.1s) | C | 60 | 17.0 | 22499 | 2021-05-18 19:18:38 | MASTER-Tavrida | (17h 48m 41.80s , +49d 49m 37.4s) | C | 60 | 15.4 | 22578 | 2021-05-18 19:19:57 | MASTER-Tavrida | (17h 44m 22.63s , +51d 42m 38.2s) | C | 60 | 15.7 | 22640 | 2021-05-18 19:20:59 | MASTER-Kislovodsk | (18h 21m 01.98s , +50d 40m 53.5s) | C | 60 | 18.0 | 22720 | 2021-05-18 19:22:19 | MASTER-Kislovodsk | (17h 45m 12.19s , +46d 54m 06.1s) | C | 60 | 18.1 | 22720 | 2021-05-18 19:22:19 | MASTER-Kislovodsk | (17h 51m 09.20s , +46d 29m 59.0s) | C | 60 | 18.9 | 22737 | 2021-05-18 19:22:37 | MASTER-Tavrida | (17h 59m 37.58s , +46d 00m 28.9s) | C | 60 | 14.3 | 22960 | 2021-05-18 19:26:20 | MASTER-Kislovodsk | (17h 39m 32.63s , +50d 19m 41.6s) | C | 60 | 18.9 | 23252 | 2021-05-18 19:31:11 | MASTER-Tavrida | (17h 42m 55.70s , +47d 55m 10.9s) | C | 60 | 16.3 | 23331 | 2021-05-18 19:32:30 | MASTER-Tavrida | (18h 01m 17.16s , +49d 47m 37.3s) | C | 60 | 16.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.