TITLE: GCN CIRCULAR NUMBER: 21219 SUBJECT: GRB 170607A: MASTER-Tavrida early OT observations DATE: 17/06/08 11:05:09 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, N.Tyurina, V.Kornilov, E.Gorbovskoy, A.Kuznetsov, V.Vladimirov, I.Gorbunov, D.Kuvshinov, A.V.Krylov, P.Balanutsa, V.V.Chazov, D. Vlasenko Lomonosov Moscow State University, Sternberg Astronomical Institut of MSU A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory N.M.Budnev, O.Gres, O. Ershova Irkutsk State University A.Gabovich, V.Yurkov, Yu.Sergienko Blagoveschensk Educational State University, Blagoveschensk D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias R.Podesta, C.Lopez, F. Podesta Observatorio Astronomico Felix Aguilar (OAFA), National University of San Juan, Argentina H. Levato, C. Saffe Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE), San Juan, Argentina MASTER-Tavrida robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in Crimea Astronomical station of Lomonosov Moscow State University pointed to the FERMI GRB 170607A error-box (ra=00 37 55 dec=+07 46 10 r=1.53, see Hamburg and Meegan GCN #21218) 25 sec after Fermi GBM notice time and 63 sec after Fermi GBM trigger time at 2017-06-08 23:19:03 UT. This was 150 sec before Swift trigger (D'Ai et al., GCN #21214). MASTER-Tavrida robotic telescope repointed to Swift BAT error box (D'Ai et al., GCN #21214) 25 sec after Swift Notice Time and 42 sec after Swift trigger at 2017-06-07 23:22:15 UT . We see OT at first image with 10 sec exposition. We have OT light curve starting before maximum (UT_max = ~ 23h 24m) up to 2017-06-08 00:40:52 UT: UT_max = 23:23:45 +/- 10sec OT unfiltered magnitude (max) = 16.4 +- 0.1 RA,DEC = 00h 29m 27s.8 + 9d 14m 35s.8 Error = 0.5 arcsec Position is coincide with UVOT position (D'Ai et al., GCN #21214). We see rebrighting or plato starting at 2017-06-07 23:52:43 UT (~30 min after Swift trigger). The message may be cited.