TITLE: GCN CIRCULAR NUMBER: 27556 SUBJECT: GRB 200412B: MASTER-Amur Optical Couterpart in Gagarin day! DATE: 20/04/12 15:47:07 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov (Lomonosov MSU) and V. Yurkov, A. Gabovich, Yu. Sergienko(Blagoveschensk Educational State University) 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(Lomonosov Moscow State University, SAI, Physics Department), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), R. Podesta, C.Lopez, F. Podesta, C.Francile(Observatorio Astronomico Felix Aguilar OAFA), H.Levato(Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE), 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), V. Yurkov, A. Gabovich, Yu. Sergienko(Blagoveschensk Educational State University) MASTER-Amur ( located near Russian Kosmodrom Vostochniy) comeback to MASTER OT J183315.33+623157.0 (Lipunov et al., GCN 27555) after 2 hours and we find optical transient with limit ~ 17.5 . So this is real afterglow: at (RA, Dec) = 18h 33m 15.33s +62d 31m 57.0s on The OT is seen in 2 images. There is no minor planet at this place. We have reference image on 2016-08-12.64123 UT with unfiltered mlim= 19.3m. Spectral observations are required. The discovery and reference images are available at: http://master.sai.msu.ru/static/OT/183315.33623157.0.png [GCN OPS NOTE(13apr20): In the first senstence, change "J111012.51+274912.8" to "J183315.33+623157.0".