TITLE: GCN CIRCULAR NUMBER: 12855 SUBJECT: XRF 120118A: early optical limit by "Pi of the Sky" DATE: 12/01/18 21:39:20 GMT FROM: Agnieszka Majczyna at Nat.Center for Nuclear Res. T.Batsch,A.Majcher,A.Majczyna,K.Nawrocki,M.Sokolowski,G.Wrochna (NCBJ, Swierk), M.Cwiok,L.W.Piotrowski,A.F.Zarnecki (University of Warsaw), K.Malek,L.Mankiewicz,R.Opiela,M.Siudek,V.Repei (CFT PAN), G.Kasprowicz,M.Zaremba (Warsaw University of Technology), from the "Pi of the Sky" collaboration ( http://grb.fuw.edu.pl ). The wide field "Pi of the Sky South" telescope, installed in the private observatory of Alain Maury in San Pedro de Atacama (http://grb.fuw.edu.pl/pi/index.html#spda_site.htm) observed field of XRF 120118A few minutes before and ~100s after the flash. No new source brighter than about 11.3 mag has been identified on 10s exposures and no source brighter than 11.7 mag on 20 coadded frames: t_start - t0 [s] t_exp start (UT) end (UT) 3-sigma limit -290 10s 06:00:14 06:00:24 11.2 +99 10s 06:06:43 06:06:53 11.3 +129 20x10s 06:07:13 06:12:12 11.7 where limit is based on the reference star magnitudo in V filter. We acknowledge great support received from Alain Maury at SPdA Observatory.