Follow-up Survey for the Binary Black Hole Merger GW200224_222234 Using Subaru/HSC and GTC/OSIRIS

Abstract

The LIGO/Virgo detected a gravitational wave (GW) event, named GW200224_222234 (also known as S200224ca) and classified as a binary-black hole coalescence, on 2020 February 24. Given its relatively small localization skymap (71 deg2 for a 90% credible region; revised to 50 deg2 in GWTC-3), we performed target-of-opportunity observations using the Subaru/Hyper Suprime-Cam (HSC) in the r2 and z bands. Observations were conducted on 2020 February 25 and 28 and March 23, with the first epoch beginning 12.3 hr after the GW detection. The survey covered the highest-probability sky area of 56.6 deg2, corresponding to a 91% probability. This was the first deep follow-up (m r ≳ 24, m z ≳ 23) for a binary-black hole merger covering >90% of the localization. By performing image subtraction and candidate screening including light-curve fitting with transient templates and examples, we found 22 off-nucleus transients that were not ruled out as the counterparts of GW200224_222234 with our Subaru/HSC data alone. We also performed GTC/OSIRIS spectroscopy of the probable host galaxies for five candidates; two are likely to be located within the 3D skymap, whereas the others are not. In conclusion, 19 transients remain as possible optical counterparts of GW200224_222234; but we could not identify a unique promising counterpart. If there are no counterparts in the remaining candidates, the upper limits of the optical luminosity are ν L ν < 5.2 − 1.9 + 2.4 × 10 41 erg s−1 and ν L ν < 1.8 − 0.6 + 0.8 × 10 42 erg s−1 in the r2 and z bands, respectively, at ∼12 hr after GW detection. We also discuss improvements in the strategies of optical follow-ups for future GW events.

Gravitational-wave Electromagnetic Counterpart Korean Observatory (GECKO): GECKO Follow-up Observation of GW190425

“…We adopt this strategy mainly for narrow FOV telescopes. Second, tiling observation covers the GW localization area with wide FOV telescopes as much as possible (e.g., Klingler et al 2019;Lundquist et al 2019;Wyatt et al 2020;Ohgami et al 2021Ohgami et al , 2023. For poorly constrained GW localization, tiling observation is more efficient than galaxy-targeted observation.…”

J-GEM electromagnetic follow-ups for gravitational-wave events in O3 and O4

“…The Japanese Collaboration for Gravitational-wave ElectroMagnetic follow-up (J-GEM) has conducted optical and NIR follow-up campaigns of GW events since 2015 [4,[12][13][14][15][16][17][18]. J-GEM consists of a consortium of facilities that cover the optical, NIR, and radio wavelengths.…”