TITLE: GCN CIRCULAR NUMBER: 20421 SUBJECT: LIGO/Virgo G268556: Lijiang Observatory GMG Telescope Upper Limit on ATLAS17aeu DATE: 17/01/10 23:03:21 GMT FROM: Mansi M. Kasliwal at Caltech A.K.H. Kong (NTHU/Oxford), J. Mao, X. Hou, J. Wang, and J.-M. Bai (YNAO) We observed the field of the optical transient ATLAS17aeu (Tonry et al., LVC GCN 20382; Kasliwal et al., GCN 20398) that is within the error region of LIGO/Virgo G268556 (LVC, GCN 20364) with the 2.4-m GMG telescope at the Lijiang Observatory in Yunnan, China. We obtained an R-band image with the Yunnan Faint Object Spectrograph and Camera (YFOSC) on 2017-01-07 14:55:35 UT. ATLAS17aeu was not detected with a 3-sigma limit of about R~23 mag. ATLAS17aeu was detected with i=21.9 mag on 2017-01-07 08:05:33 UT (Kasliwal et al., GCN 20398) and was proposed to be the afterglow of GRB 170105A. Our observation indicates that the source is fainter than the suggested power-law decay. However, due to the use of different filters in ATLAS, Palomar, and Lijiang, the lightcurve should be treated with caution.