Journal Article

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

Simunovic, Mirko, Utsumi, Yousuke, The J-GEM collaboration , The J-GEM collaboration, Acosta-Pulido, Jose Antonio, Tanaka, Ichi, Banerjee, Smaranika, Poidevin, Frédérick, Ohgami, Takayuki, Akitaya, Hiroshi, Muñoz-Darias, Teo, Takagi, Yuhei, Terai, Tsuyoshi, Sasada, Mahito, Niino, Yuu, Yanagisawa, Kenshi, Tominaga, Nozomu, González, Josefa Becerra, Yoshida, Michitoshi, Ohsawa, Ryou, Morokuma, Tomoki, Tanaka, Masaomi, Pérez-Fournon, Ismael

2023

Overview

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 νLν<5.2−1.9+2.4×1041 erg s−1 and νLν<1.8−0.6+0.8×1042 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.

• Publisher: IOP Publishing
• Subject: Black holes / Curve fitting / Galaxies / Gravitational waves / Localization / Luminosity / Optical counterparts (astronomy) / Sky surveys (astronomy) / Spectroscopy / Transients (astronomy)