TITLE: GCN CIRCULAR NUMBER: 23143 SUBJECT: GRB 180728A: MASTER early polarization and 19 days monitoring DATE: 18/08/16 20:33:39 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, N.Tiurina, D.Vlasenko, V.Kornilov, A.Kuznetsov, V.Chazov, I. Gorbunov, 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 (BSPU) MASTER Global Robotic Net ( Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) inspected GRB 180728A (SwiftBAT GRB discovery : Starling et al. GCN 23046; MASTER optical counterpart discovery: Lipunov et al. GCN 23048;GCN23050; SwiftXRT: Perri et al. GCN 23049; Redshift, VLT: Rossi et al. GCN 23055; SN discovery,VLT: Izzo et al. GCN 23142). every night since the discovery. There are unfiltered limits at MASTER images and absolute magnitude of SN ( Izzo et al. GCN 23142) for Omega_Vac = 0.7 and H_0 = 70 km/s/Mpc and Galactic extinction 0.1 for our red ccd: Date_Time,UT | Exp,s | MASTER-Site | m_lim| M 2018-07-29 21:18:37.092 | 2340 | MASTER-SAAO | 21.8 | -16.3 2018-07-30 21:07:24.839 | 1440 | MASTER-SAAO | 20.8 | -17.3 2018-07-30 21:07:24.912 | 1440 | MASTER-SAAO | 21.4 | -16.7 2018-08-01 19:11:32.906 | 1620 | MASTER-SAAO | 20.9 | -17.2 2018-08-01 19:15:07.977 | 1620 | MASTER-SAAO | 20.9 | -17.2 2018-08-02 17:03:40.025 | 3780 | MASTER-SAAO | 20.8 | -17.2 2018-08-02 18:12:49.446 | 3960 | MASTER-SAAO | 20.9 | -17.2 2018-08-03 17:53:21.097 | 4140 | MASTER-SAAO | 20.8 | -17.3 2018-08-03 17:53:21.347 | 4140 | MASTER-SAAO | 21.1 | -17.0 2018-08-03 23:21:10.842 | 3420 | MASTER-OAFA | 20.6 | -17.5 2018-08-04 17:05:35.120 | 2700 | MASTER-SAAO | 20.9 | -17.2 2018-08-04 17:12:46.879 | 2880 | MASTER-SAAO | 20.8 | -17.3 2018-08-04 23:07:09.154 | 720 | MASTER-OAFA | 20.5 | -17.6 2018-08-05 22:18:29.225 | 3240 | MASTER-SAAO | 20.8 | -17.3 2018-08-05 22:22:04.704 | 3240 | MASTER-SAAO | 21.1 | -17.0 2018-08-05 23:08:46.934 | 1260 | MASTER-OAFA | 21.5 | -16.5 2018-08-06 18:46:19.565 | 3600 | MASTER-SAAO | 20.8 | -17.3 2018-08-06 18:46:19.605 | 3600 | MASTER-SAAO | 20.8 | -17.3 2018-08-07 00:26:41.653 | 900 | MASTER-OAFA | 20.4 | -17.7 2018-08-07 03:30:36.096 | 2520 | MASTER-OAFA | 20.6 | -17.5 2018-08-07 17:15:34.447 | 3780 | MASTER-SAAO | 20.9 | -17.2 2018-08-07 18:23:07.857 | 3780 | MASTER-SAAO | 21.7 | -16.4 2018-08-08 17:59:05.042 | 4140 | MASTER-SAAO | 20.8 | -17.3 2018-08-08 18:02:42.597 | 4140 | MASTER-SAAO | 20.9 | -17.2 2018-08-08 23:11:34.904 | 3240 | MASTER-OAFA | 21.9 | -16.2 2018-08-09 18:55:17.807 | 540 | MASTER-SAAO | 20.8 | -17.2 2018-08-09 18:58:54.517 | 540 | MASTER-SAAO | 20.8 | -17.2 2018-08-09 23:04:26.723 | 3240 | MASTER-OAFA | 20.5 | -17.5 2018-08-10 17:00:41.943 | 2520 | MASTER-SAAO | 20.9 | -17.1 2018-08-11 00:08:05.570 | 4500 | MASTER-OAFA | 20.7 | -17.3 2018-08-11 18:43:29.720 | 7020 | MASTER-SAAO | 20.9 | -17.1 2018-08-11 23:12:32.140 | 3240 | MASTER-OAFA | 20.6 | -17.4 2018-08-12 19:46:57.192 | 7560 | MASTER-SAAO | 22.1 | -15.9 2018-08-12 19:46:57.246 | 7560 | MASTER-SAAO | 20.9 | -17.1 2018-08-12 23:18:02.053 | 3240 | MASTER-OAFA | 19.8 | -18.2 2018-08-13 07:43:55.504 | 3420 | MASTER-OAFA | 21.2 | -16.8 We have carried out preliminary photometry of MASTER early observations (Lipunov et al. GCN 23048; GCN23050;) also we report about considerable polarization of optical radiation of gamma burst the first minute after its beginning. This message can be cited.