TITLE: GCN CIRCULAR NUMBER: 23007 SUBJECT: Fermi Trigger 553879512: MASTER optical observation DATE: 18/07/22 08:41:48 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, N.Tiurina, E. Gorbovskoy, V.Kornilov, A.Kuznetsov, V.Chazov, I. Gorbunov, D.Zimnukhov, D.Kuvshinov, P.Balanutsa, V.Vladimirov, D. Vlasenko Lomonosov Moscow State University,SAI D. Buckley, South African Astronomical Observatory (SAAO) R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias (IAC) A. Tlatov, V.Senik, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory R. Podesta, F. Podesta, C. Lopez, C.Francile Observatorio Astronomico Felix Aguilar (OAFA) H.Levato, Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) O. Gres, N.M.Budnev , Yu.Ishmuhametova Irkutsk State University (ISU) A. Gabovich, V. Yurkov, Yu. Sergienko Blagoveschensk Educational State University (BSPU) MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in SAAO was starting survey on the Fermi Trigger 553879512 ("GRB180721.64") error-box (ra=15 11 04 dec=+18 32 22 r=9.93) 6541 sec after notice time and 6591 sec after trigger time at 2018-07-21 17:14:58 UT. The 5-sigma upper limit on our first (60s exposure) set is about 18.8 mag The observations made on zenit distance = 52 degrees, galaxy latitude b = 56 degree. The moon (69 % bright part) is 68 degrees above the horizon. The distance between moon and object is 32 The sun altitude is -17.5 degree. The object can be observed till sunrise at 2018-07-22 05:31:50. MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in IAC was starting survey on the Fermi Trigger 553879512 ("GRB180721.64") error-box (ra=15 11 04 dec=+18 32 22 r=9.93) 19242 sec after notice time and 19291 sec after trigger time at 2018-07-21 20:46:39 UT. The 5-sigma upper limit on our first (60s exposure) set is about 17.0 mag The observations made on zenit distance = 12 degrees, galaxy latitude b = 56 degree. The moon (70 % bright part) is 48 degrees above the horizon. The distance between moon and object is 32 Observations started at twilight. The sun altitude is -9.7 degree. The object can be observed till 2018-07-22 03:02:12. MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in OAFA was starting survey on the FERMI GRB180721.64 error-box (ra=15 11 04 dec=+18 32 22 r=9.93) 28298 sec after notice time and 28347 sec after trigger time at 2018-07-21 23:17:35 UT. The 5-sigma upper limit on our first (60s exposure) set is about 14.0 mag The observations made on zenit distance = 51 degrees, galaxy latitude b = 56 degree. The moon (71 % bright part) is 68 degrees above the horizon. The distance between moon and object is 33 The sun altitude is -17.7 degree. The object can be observed till 2018-07-22 05:03:37 The message may be cited.