TITLE: GCN CIRCULAR NUMBER: 36343 SUBJECT: LIGO/Virgo/KAGRA S240422ed: GECKO/KMTNet ToO observations DATE: 24/04/29 12:29:25 GMT FROM: Mankeun Jeong jmk5040@gmail.com
Mankeun Jeong, Myungshin Im, Gregory S. H. Paek, Seo-Won Chang, Seong-Kook Lee (SNU/SNU ARC), Dong-Jin Kim and Chung-Uk Lee (KASI), on behalf of the GECKO team
We report on the observations conducted by the GECKO team using the three Korea Microlensing Telescope Network (KMTNet) 1.6-m telescopes equipped with 4 square degree cameras in response to the LIGO/Virgo/KAGRA S240422ed trigger (GCN 36236). Observations commenced on 2024-04-23 00:54:26 UTC, approximately 3.3 hours after the event, utilizing the Johnson-Coursin R band. Our efforts resulted in coverage of 232 sq. degrees of the localization area. The spatial extent of our observations is detailed in TreasureMap (Wyatt et al. 2020; https://treasuremap.space/alerts?graceids=S240422ed).
For each field, we conducted 4×120 sec exposures, revisiting each target field twice. This strategy achieved a depth between 20.4 and 22.2 AB magnitudes with a 5-sigma detection limit for each visit. For the subtraction process, we utilized template images from the KMTNet Synoptic Survey of Southern Sky (KS4), taken before the gravitational wave detection. The overlapping area between our observed regions and the KS4 templates is approximately 60 sq. degrees. In areas without KS4 coverage, we employed PS1 templates to facilitate transient searches around GLADE+ galaxies (Dalya et al., 2022).
Additional measures included cross-matching our candidate detections with the Minor Planet Center database to identify known asteroids and exclude recognized sources. The integration of machine learning algorithms is also underway to refine the detection process. Data reduction and analysis are ongoing, and further updates will be provided as new results become available.
Gravitational-wave EM Counterpart Korean Observatory (GECKO; Im et al. 2023, Proceedings of IAU Symp. Vol. 363, pp. 207.; Paek et al. 2024, The Astrophysical Journal, Vol. 960, Number 2, 113.) is a network of 0.5m to 1m class telescopes worldwide. KMTNet is operated by the Korea Astronomy and Space Science Institute. We thank the KMTNet operators for their support for the KMTNet observations.
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