TITLE: GCN CIRCULAR NUMBER: 24193 SUBJECT: LIGO/Virgo S190425z: Lulin Follow-Up Observations DATE: 19/04/25 19:55:03 GMT FROM: Mansi M. Kasliwal at Caltech/Carnegie Han-Jie Tan (NCU), Po-Chieh Yu (NCU), Chow-Choong Ngeow (NCU), Wing-Huen Ip (NCU) On behalf of Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations We report the photometric measurements of two promising candidates ZTF19aarykkb and ZTF19aarzaod (GCN 24191) associated with the gravitational wave trigger S190425z (GCN 24168) using Lulin One-meter Telescope(LOT) in Taiwan. The observations were conducted using g, r, i filters at 2019-04-25 15:57:19 UT, ~7.65 hours after the trigger, and 2019-04-25 17:25:43, ~9.12 hours after the trigger, respectively. Preliminary photometry were obtained by calibrating with Pan-STARRS catalog. We would like to thank the staff in Lulin Observatory for helping the observations. Summary of ZTF19aarykkb: UT Filter Exp(s) Mag (AB) 2019-04-25 15:58:49 g 180 18.84+/-0.04 2019-04-25 16:02:11 r 180 18.23+/-0.02 2019-04-25 16:05:33 i 180 17.92+/-0.02 Summary of ZTF19aarzaod: 2019-04-25 17:48:24 g 300 21.45+/0.47 2019-04-25 17:53:45 r 300 20.26+/-0.25 2019-04-25 17:41:56 i 300 19.93+/-0.13 Also, we searched for optical counterpart in 90% localization area of LIGO/Virgo S190425z (GCN 24168). The observation started at 2019-04-25 12:27:23 UT, 249 minutes after the trigger, and 27 galaxies were observed in R-band with 180 second exposure time. No obvious transient can be identified brighter than R~20 mag (AB). The galaxy coordinates are listed below. RA(deg) DEC(deg) 194.9152 +53.341 212.0897 +55.302 212.6985 +35.913 213.2136 +35.711 213.6132 +36.404 216.0865 +36.461 217.9843 +33.643 218.3270 +34.735 219.1718 +34.973 232.4191 +30.486 235.3749 +27.986 236.0957 +25.327 236.3709 +26.603 236.9752 +25.729 239.0161 +24.448 239.2193 +24.662 239.2199 +25.569 239.6450 +27.618 239.7168 +26.136 239.9651 +25.941 241.1394 +23.838 241.2978 +24.960 242.2803 +21.868 242.7183 +22.626 242.8088 +26.923 242.8782 +23.812 243.0847 +23.002