Searching for electromagnetic emission in an AGN from the gravitational wave binary black hole merger candidate S230922g
Tomás Cabrera, A. Palmese, Lei Hu, Brendan O’Connor, K. E. Saavik Ford, Barry McKernan, Igor Andreoni, Tomás Ahumada, Ariel Amsellem, Malte Busmann, P. Clark, M. W. Coughlin, Ekaterine Dadiani, Verónica Marín Díaz, M. J. Graham, D. Gruen, Keerthi Kunnumkai, Jake Postiglione, A. Riffeser, Julian S. Sommer, F. Valdés
Abstract
We carried out long-term monitoring of the LIGO/Virgo/KAGRA binary black hole (BBH) merger candidate S230922g in search of electromagnetic emission from the interaction of the merger remnant with an embedding active galactic nuclei (AGN) accretion disk. Using a dataset primarily composed of wide-field imaging from the Dark Energy Camera and supplemented by additional photometric and spectroscopic resources, we searched $\ensuremath{\sim}70%$ of the sky area probability for transient phenomena and discovered six counterpart candidates. One especially promising candidate---AT 2023aagj---exhibited temporally varying asymmetric components in spectral broad line regions, a feature potentially indicative of an off-center event such as a BBH merger. This represents the first live search and multiwavelength, photometric, and spectroscopic monitoring of a gravitational wave BBH optical counterpart candidate in the disk of an AGN.