TITLE: GCN CIRCULAR NUMBER: 10700 SUBJECT: GRB 100418A: RTT150 optical observations DATE: 10/04/28 21:04:18 GMT FROM: Irek Khamitov at TUG I. Bikmaev (KSU/AST), I. Khamitov (TUG), S. Melnikov, N. Sakhibullin (KSU/AST), R. Burenin, M. Pavlinsky, R. Sunyaev (IKI), Z. Eker (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.) report: The optical afterglow of GRB 100418A (Marshall et al., GCN 10612, Filgas et al., GCN 10617) was observed with Russian-Turkish 1.5-m telescope (RTT150, Bakirlitepe, TUBITAK National Observatory, Turkey) in April 23/24 and April 27/28, 2010, in partially cloudy conditions. We obtained one useful 900 sec image in Rc-band in April 24 and nine 900 sec images in April 28. In spite of bright Moon in April 27/28 observations OT is clearly detected in combined image. In the Table below we give our Rc estimates of the OT brightness relative to the nearby USNO-B1.0 star 1014-0271368 (R2Mag=17.32). Date UT (T-T0),h Rc err Apr.24 00:20 123.1 20.6 +/-0.10 Apr.28 00:50 220.0 21.25 +/-0.05 Preliminary Rc-light curve can be found at: http://hea.iki.rssi.ru/grb/100418a/indexeng.html OT is still brighter compared with its host galaxy (Malesani, GCN10621) and further spectroscopic and photometric observations of this event are very important to check possible SN contribution in the OT flux. -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.