TITLE: GCN CIRCULAR NUMBER: 24285 SUBJECT: LIGO/Virgo S190425z: CNEOST Optical Observations DATE: 19/04/27 15:02:40 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 conducted optical imaging observations for gravitational wave alert with Chinese Near Earth Object Survey Telescope (CNEOST) at Xuyi astronomical station in Jiangsu Province, China (32.75N, 118.47E). The information of observations and preliminary results are listed below. Alert: LIGO/Virgo S190425z (GCN 24168) StartTime (UT): 2019-04-26T11:49:02.152 EndTime (UT): 2019-04-26T16:36:13.239 Skycover (Square Degree): 675.0 Telescope FoV (Square Degree): 9.0 # id CentRA(Degree) CentDEC(Degree) LimiteMag3\sigma 5\sigma 10\sigma Filter 1 184.785507 26.824320 20.983 19.969 19.190 VR 2 192.873947 29.601379 20.944 19.900 19.114 VR 3 191.960449 32.390297 20.907 19.837 19.004 VR 4 183.234314 29.591774 21.019 19.959 19.177 VR 5 179.964020 21.201527 20.947 19.945 19.179 VR 6 187.898514 26.821241 20.979 19.949 19.173 VR 7 196.073746 29.603632 20.851 19.799 18.974 VR 8 189.684692 29.626089 20.875 19.864 19.036 VR 9 180.602478 23.990540 21.003 19.962 19.217 VR 10 184.785507 26.824320 20.983 19.969 19.190 VR 11 192.873947 29.601379 20.944 19.900 19.114 VR 12 191.960449 32.390297 20.907 19.837 19.004 VR 13 183.234314 29.591774 21.019 19.959 19.177 VR 14 198.608170 32.404903 21.028 19.933 19.087 VR 15 208.536697 32.404457 21.031 19.898 18.917 VR 16 215.425766 35.189808 20.952 19.912 18.869 VR 17 211.972580 35.169170 21.062 19.993 19.055 VR 18 201.739838 35.234352 21.097 20.013 19.149 VR 19 198.608170 32.404903 21.028 19.933 19.087 VR 20 208.536697 32.404457 21.031 19.898 18.917 VR 21 215.425766 35.189808 20.952 19.912 18.869 VR 22 211.972580 35.169170 21.062 19.993 19.055 VR 23 201.739838 35.234352 21.097 20.013 19.149 VR 24 201.873154 32.386822 21.000 19.912 19.094 VR 25 211.837280 32.391037 21.018 19.956 18.887 VR 26 216.216324 37.998722 21.074 19.972 18.897 VR 27 208.568130 35.197506 21.055 19.976 19.012 VR 28 198.301239 35.218636 21.127 20.040 19.123 VR 29 218.851593 35.218647 21.162 20.061 19.121 VR 30 222.244431 35.193432 21.146 20.100 19.256 VR 31 225.679306 35.158276 21.108 20.102 19.138 VR 32 229.114594 35.154079 21.109 20.069 19.083 VR 33 225.053543 29.585041 21.109 20.064 19.101 VR 34 218.484024 32.397865 21.157 20.051 19.053 VR 35 223.324417 38.002777 21.197 20.108 19.214 VR 36 225.081039 32.366611 21.100 20.031 19.062 VR 37 230.409027 37.977615 20.998 19.982 19.029 VR 38 228.267899 29.562998 21.050 20.002 19.011 VR 39 218.608292 29.590960 21.086 20.021 19.093 VR 40 219.784576 38.000137 21.168 20.108 19.188 VR 41 221.790970 32.360126 21.181 20.079 19.201 VR 42 226.883743 37.952568 21.151 20.092 19.148 VR 43 228.391403 32.370419 21.037 19.996 18.972 VR 44 221.833221 29.593536 21.120 20.102 19.196 VR 45 231.493652 29.561152 21.107 20.079 19.090 VR 46 233.963348 37.967670 21.103 20.118 19.248 VR 47 239.815979 40.776882 21.177 20.151 19.176 VR 48 235.000549 32.369446 21.087 20.096 19.212 VR 49 235.720306 23.978613 21.080 20.069 19.117 VR 50 231.493652 29.561152 21.107 20.079 19.090 VR 51 233.963348 37.967670 21.103 20.118 19.248 VR 52 239.815979 40.776882 21.177 20.151 19.176 VR 53 235.000549 32.369446 21.087 20.096 19.212 VR 54 235.720306 23.978613 21.080 20.069 19.117 VR 55 231.493652 29.561152 21.107 20.079 19.090 VR 56 233.963348 37.967670 21.103 20.118 19.248 VR 57 239.815979 40.776882 21.177 20.151 19.176 VR 58 235.000549 32.369446 21.087 20.096 19.212 VR 59 235.720306 23.978613 21.080 20.069 19.117 VR 60 238.067291 26.742233 21.075 20.070 19.136 VR 61 239.365143 35.179752 21.189 20.223 19.336 VR 62 244.608307 37.976181 21.162 20.188 19.205 VR 63 241.650742 32.340134 21.133 20.164 19.229 VR 64 241.823608 23.950287 21.047 20.079 19.143 VR 65 238.767471 23.968771 21.065 20.090 19.152 VR 66 238.319641 32.363117 21.178 20.198 19.319 VR 67 243.497925 40.747852 21.083 20.105 19.182 VR 68 242.779221 35.157001 21.160 20.204 19.243 VR 69 241.178314 26.761927 21.091 20.087 19.140 VR 70 236.980118 21.171730 21.104 20.122 19.199 VR 71 237.881577 29.548300 21.096 20.133 19.217 VR 72 241.073135 37.950817 21.136 20.129 19.225 VR 73 246.223633 35.124283 21.138 20.113 19.161 VR 74 241.141617 29.572805 21.075 20.098 19.182 VR 75 240.004684 21.128513 21.015 20.035 19.122 VR Our vetting procedure based on image difference and machine learning have identified some known sources (thus unrelated to the GW event) such as OPEM-19fl = AT 2019dje OPEM-19fj = SN 2019dek OPEM-19fi = SN 2019dhc OPEM-19fh = SN 2019dkx OPEM-19fg = SN2019cdc OPEM-19ff = AT 2019dku OPEM-19fe = SN 2019dod OPEM-19ex = AT 2019dzt OPEM-19ev = AT 2018kud OPEM-19eu = AT 2019dxm OPEM-19eu = AT 2019dxm OPEM-19en = AT 2019cya = ATLAS19ggy = ZTF19aaoyech OPEM-19em = AT 2018ivk No interesting transient can be reported here. Detailed data analysis is still in progress and any interesting transient will be reported later.