TITLE: GCN CIRCULAR NUMBER: 31620 SUBJECT: IceCube Alert 220220.60:NuEm-220220A: MASTER optical possible counterpart DATE: 22/02/21 10:09:51 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs O.Gress & N.M. Budnev (Irkutsk State University, API), V. Lipunov, N.Tiurina, K.Zhirkov, A.Kuznetsov, P.Balanutsa, A.Chasovnikov, K.Zhirkov, N.Tiurina, G.Antipov, E.Gorbovskoy, D. Vlasenko, V.Senik, Ya.Kechin, V.Topolev (Lomonosov MSU,SAI,PhysicsDepartment), A. Gabovich & V.Yurkov (Blagoveschensk Educational StateUniversity) L. Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J. Martinez, A.R.Corella, L.H.Rodriguez (INAOE, OAGH), C.Francile, R. Podesta, F. Podesta (OAFA), R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), MASTER Global Robotic Net (Lipunov et al. 2010, Advances in Astronomy, v.2010, 30L) started IceCube 20220220.60/AMON NuEm-220220A alert (GCN #31615, https://gcn.gsfc.nasa.gov/other/icecube_220220A.gcn3 ) optical observations 25 sec after notice time (618s after trigger time) at 2022-02-20 14:29:55 UT at MASTER-Amur (Lipunov et al. GCN #31616) and observed it in MASTER-OAGH (Mexico), -SAAO (South Africa), -OAFA (Argentina), see cover map https://master.sai.msu.ru/site/master2/event.php?id=1889478
There is a blazar 5BZBJ1442+1200 (RA=220.70117d DEC=12.01119d) 1.5 degrees from the center of the event that shows moderate dimming that started 10 days before the neutrino according to public ATLAS data (https://fallingstar-data.com/forcedphot/queue/169872/plot.pdf).
There was IC-201014A in this region (IC GCN #28624, MASTER GCN #28627 ). Due to this dimming we are inclined to believe that 5BZBJ1442+1200 might be a source of NuEM-220220A even though it is largely outside the error-box. The analysis will be continued. Additional observations are planned.