TITLE:   GCN CIRCULAR
NUMBER:  33985
SUBJECT: LIGO/Virgo/KAGRA S230615az: Non-Detections of GROWTH-India Candidates from GECKO Optical Observations
DATE:    23/06/17 13:54:22 GMT
FROM:    Gregory Paek at Seoul National University <gregorypaek94@gmail.com>

Gregory S.-H. Paek (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), and Hyun-Il Sung (KASI), on behalf of the GECKO Team

We report the optical observations conducted with the LOAO telescopes of two optical counterpart candidates, GIT230615aa, and GIT230615ab (H. Kumar, GCN 33974) of the LIGO/Virgo/KAGRA gravitational-wave event, S230615az. The LOAO is a 1.0-meter class telescope in the USA. The LOAO observation started at 2023-06-16 05:03 (UT) or about 0.46 days after the GW alert in R-band. We calibrated flux with the PANSTARRS catalog and used an AB magnitude system. As a result, we could not detect any significant signals from the candidates. Furthermore, observations taken approximately 0.8 days after the GW alert also reported the non-detection of both candidates (Z.P. Zhu, GCN 33981). The preliminary 5 sigma depths of these images are below:

OBJECT      DATE-OBS[UTC]       t-t0[days] FILTER EXPTIME DEPTH
GIT230615aa 2023-06-16T05:03:20 0.46       R      180s*10 21.0
GIT230615ab 2023-06-16T05:23:51 0.48       R      180s*10 20.8

Gravitational-wave EM Counterpart Korean Observatory (GECKO) is a network of 10+ 0.5m to 1m class telescopes worldwide. The Korea Astronomy and Space Science Institute operates LOAO. We thank the LOAO operators for their support for the observations.