TITLE: GCN CIRCULAR NUMBER: 24647 SUBJECT: LIGO/Virgo S190521r: One optical transient from CNEOST DATE: 19/05/22 02:11:08 GMT FROM: Dong Xu at NAOC/CAS Bin Li, Hai-bin Zhao (PMO), Dong Xu, Zi-pei Zhu, Bang-Yao Yu,Tian-meng Zhang, Xu Zhou, Chen-zhou Cui, Hui-juan Wang (NAOC), Xue-feng Wu, Zhi-ping Jin, Tian-rui Sun, Hao Lu, Ge-tu Zhaori, Ren-quan Hong, Long-fei Hu (PMO), Xiao-feng Wang, Wen-xiong Li (THU), Li-fan Wang (PMO/TAMU), Jin-zhong Liu (XAO), Ji-rong Mao, Jin-ming Bai (YNAO), report on behalf of the CNEOST collaboration We performed the search for the optical counterpart of LIGO/Virgo S190521r (LVC, GCN 24632) with the Chinese Near Earth Object Survey Telescope (CNEOST) at Xuyi, Jiangsu, China. The 3 x 3 deg^2 imager scanned high probability regions of the LVC localization that are accessible to CNEOST. Statistical results on the search will be reported later, and here we report an optical transient. The OT is localised at coordinates: R.A. (J2000) = 17:19:41.85 Dec. (J2000) = +01:04:45.19 with an uncertainty of ~ 0.5 arcsec. The OT had m(VR) ~ 17.8 mag at 15:48:04 UT on 2019-05-21, and appeared at the above position in three images with time interval of ~ 40 mins. At the above position, there exists a very low S/N object in the PanSTARRS and SDSS surveys. The object had m(r) ~ 23.3 mag, and seems extended to some extent. Verification of the OT is encouraged.