GCN Circular 21219

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.