TITLE: GCN CIRCULAR NUMBER: 10398 SUBJECT: GRB 100205A: BOAO/LOAO zYJK observation DATE: 10/02/09 14:50:50 GMT FROM: Myungshin Im at Seoul Nat U M. Im, Y. Jeon, W. Park (CEOU/Seoul National Univ), H.-I. Sung (KASI) and Y. Urata (NCU) on behalf of EAFON team. We observed the GRB100205A (GCN 10361 Racusin et al.) with J and K-band using KASINICS instrument on the 1.8m telescope at the Bohyunsan Optical Astronomy Observatory (BOAO), Korea, starting from 2010-02-05, 17:28:13 UT. We also observed the GRB with z and Y filters using the LOAO 1-m telescope, starting from 2010-02-05, 10:37:51 UT. We do not detect the afterglow at the reported position (GCN 10361.; GCN 10366, Tanvir et al.) in any of the bands with the upper limits summarized below. Our non-detection in K suggests that the afterglow candidate faded since the report of the K-band detection (GCN 10366; GCN 10374 Cucchiara et al.), confirming that it is an afterglow. The values for J and K-bands are preliminary, and we are refining the photometry. The data analysis of the 2nd night follow-up observation (z,Y) is on-going. Filter z Y J K ------------------------------------------------- 3-sigma limit (AB) 22.3 20.8 22.3 22.5 mid-point(UT,hh:mm) 12:11 11:07 17:43 19:01 We thank the LOAO operator, J. Yoon for his assistance for this observation.