TITLE: GCN CIRCULAR NUMBER: 22273 SUBJECT: GRB 171222A: MASTER-Net OT observations DATE: 17/12/23 11:26:55 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs N.Tyurina, V. Lipunov, E. Gorbovskoy,V.Kornilov, D.Kuvshinov, A.V.Krylov, I.Gorbunov, P.Balanutsa, A.Kuznetsov, V.V.Chazov, D. Vlasenko Lomonosov Moscow State University, Sternberg Astronomical Institut of MSU 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 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 O.Gres, K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk, Irkutsk State University V.Yurkov, Yu.Sergienko Blagoveschensk Educational State University, Blagoveschensk A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory MASTER-IAC robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in IAC (Tenerife) was pointed to the Swift GRB171222A (Racusin et al., GCN #22265;) 47159 seconds (~ 13h ) after trigger time at 2017-12-23 05:31:03 UT. The 5-sigma upper limit has been about 19.3 at single (180 s) and 20.9 at coadd (10x180 = 1800 s ) images. We see OT detected by (Perley et al., GCN #22269; de Ugarte Postigo et al., GCN #22272 ) at X-ray position (Osborne et al., GCN #22266; D'Elia et al., GCN #22271). The OT unfiltered magnitude is about ~ 21. The observations made on zenit distance = 11 degrees, galaxy latitude b = 52 degree. The moon (21 % bright part) below the horizon (The altitude of the Moon is -73 degree ). The sun altitude is -30.5 degree. The object can be observed till sunrise at 2017-12-23 07:54:43 . This message can be cited.