TITLE: GCN CIRCULAR NUMBER: 35791 SUBJECT: Transient EPW20240219aa: GECKO: LOAO Optical Upper Limits DATE: 24/02/25 16:11:06 GMT FROM: Gregory Paek at Seoul National University <gregorypaek94@gmail.com> Gregory S.H. Paek (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Chung-Uk Lee (KASI), Seung-Lee Kim (KASI), Hyun-Il Sung (KASI) on behalf of a larger collaboration We searched for the optical counterpart of the bright X-ray flare, EPW20240219aa (Zhang et al., ATel #16463; Zhang et al., GCN #35773) with the 1-m class telescope in Lemonsan Optical Astronomy Observatory (LOAO), one of the facilities of the GW EM-Counterpart Korean Observatory (GECKO). We observed the localization center provided by the Wide-field X-ray Telescope (WXT) modules aboard the Einstein Probe (EP) mission at RA, Dec = 80.016 deg, 25.541 deg, but could not find any transient within the field of view of LOAO (28.1'x28.1'). We calibrated flux with the PS1 catalog and used an AB magnitude system. ------ Filter Date-obs[UT] Exp.time[s] Depth(5sigma) R 2024-02-23T02:46:34 60*30 20.562 We thank the LOAO operator for performing the observation. Gravitational-wave Electromagnetic-wave Counterpart Korean Observatory (GECKO) is a network of 10+ 0.5m to 1m class telescopes over the world. View this GCN Circular online at https://gcn.nasa.gov/circulars/35791. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...