TITLE: GCN CIRCULAR NUMBER: 22942 SUBJECT: IceCube-170922A: First Optical observations of the Neutrino Trigger by MASTER Global Net and 25 IceCube alerts inspection. DATE: 18/07/12 16:51:56 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tiurina, A.Kuznetsov, V.Chazov, I. Gorbunov, D. Vlasenko, D.Zimnukhov, D.Kuvshinov, P.Balanutsa, V.Vladimirov 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, Blagoveschensk MASTER-Tavrida robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in Crimea was pointed to the IceCube-170922A (Kopper et al. GCN #21916; ) 27 sec after notice time and 73 sec after trigger time at 2017-09-22 20:55:43 UT. On our first (180s exposure) set we cleary detected TXS 0506+056 within ICECUBE error-box (ra=77.2833 dec=5.75139 r=0.25). The 5-sigma upper limit has been about 17.5 mag on single and 19.5 on coadd images. Since 2017-09-22 20:55:43 (i.e 73 sec after trigger) till 2017-09-18 we have ~ 300 observations provided by MASTER-Tavrida, MASTER-SAAO, MASTER-OAFA, MASTER-Kislovodsk and MASTER-Blagoveschensk. The object zenith distance was 84 degree at a time of first observations and it was rise. Unfortunately, we were extremely busy at this time handling the kiln on August 17, 2017, which we detected independent of the Chilean telescopes (Abbot et al 2017ApJ...848L..12A; Lipunov et al. 2017ApJ...850L...1L). Our telescopes react to 25 IceCube neutrino alerts ( 5874 images!), starting with the famous neutrino triplet in whose publication we participate and made a decisive contribution to the optical inspection (Aartsen et al 2017, A&A, Vol 607, A115, DOI: 10.1051/0004-6361/201730620) Just in case, we report that we have previous, synchronous and subsequent optical observations of the ICECube neutrino alert on June 2018. Just in case, we report that we have precursor and synchronous observations of the neutrino alert of June 2018 with QSO inside 2 sigma error box. The message may be cited.