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Searching for Electromagnetic Counterpart Candidates to GW231123

Lei He, Liang-Gui Zhu, Zheng-Yan Liu, Rui Niu, Chao Wei, Bing-Zhou Gao, Ming-Shen Zhou, Run-Duo Liang, Ken Chen, Jian-Min Wang, Ning Jiang, Zhen-Yi Cai, Ji-an Jiang, Zi-Gao Dai, Ye-Fei Yuan, Jian Li, Wen Zhao

TL;DR

The paper investigates an electromagnetic counterpart to GW231123 by crossmatching LVK localization with a ZTF-derived AGN flare catalog to search for post-trigger optical flares. Using forced photometry with an extended baseline and a Gaussian process flare detector, the authors identify six candidate AGN flares that are spatially and temporally consistent with the GW event and fit them with a rise–decay model to apply selection criteria. They assess association strength with Bayesian odds ratios across multiple GW waveform models, finding strong evidence for most candidates in at least one model, though none are conclusively confirmed. Interpreting the results within an AGN-disk BBH merger framework, they show how disk properties and recoil dynamics could shape the observed flares, while highlighting the need for rapid, multi-wavelength follow-up and spectroscopy to confirm a true EM counterpart.

Abstract

The detection of GW231123, a gravitational-wave (GW) event with exceptionally massive and rapidly spinning black holes, suggests the possible formation within an active galactic nucleus (AGN) disk, which provides a favorable environment for potentially generating an observable electromagnetic (EM) counterpart. We conduct a search for such a counterpart by crossmatching the GW localization with a comprehensive catalog of AGN flares from the Zwicky Transient Facility. Our analysis yields six plausible optical flare candidates that are spatially and temporally coincident with GW231123 and exhibit significant deviations from their AGN baseline flux. Although these candidates represent a crucial first step, their true nature remains inconclusive. Confirming any one of these flares via future observations would provide a landmark validation of the AGN formation channel and unlock the multi-messenger potential of this extraordinary merger.

Searching for Electromagnetic Counterpart Candidates to GW231123

TL;DR

The paper investigates an electromagnetic counterpart to GW231123 by crossmatching LVK localization with a ZTF-derived AGN flare catalog to search for post-trigger optical flares. Using forced photometry with an extended baseline and a Gaussian process flare detector, the authors identify six candidate AGN flares that are spatially and temporally consistent with the GW event and fit them with a rise–decay model to apply selection criteria. They assess association strength with Bayesian odds ratios across multiple GW waveform models, finding strong evidence for most candidates in at least one model, though none are conclusively confirmed. Interpreting the results within an AGN-disk BBH merger framework, they show how disk properties and recoil dynamics could shape the observed flares, while highlighting the need for rapid, multi-wavelength follow-up and spectroscopy to confirm a true EM counterpart.

Abstract

The detection of GW231123, a gravitational-wave (GW) event with exceptionally massive and rapidly spinning black holes, suggests the possible formation within an active galactic nucleus (AGN) disk, which provides a favorable environment for potentially generating an observable electromagnetic (EM) counterpart. We conduct a search for such a counterpart by crossmatching the GW localization with a comprehensive catalog of AGN flares from the Zwicky Transient Facility. Our analysis yields six plausible optical flare candidates that are spatially and temporally coincident with GW231123 and exhibit significant deviations from their AGN baseline flux. Although these candidates represent a crucial first step, their true nature remains inconclusive. Confirming any one of these flares via future observations would provide a landmark validation of the AGN formation channel and unlock the multi-messenger potential of this extraordinary merger.

Paper Structure

This paper contains 8 sections, 4 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Data and Searching Method
  3. GW data and AGN flares
  4. Searching method
  5. Results
  6. Discussion
  7. Conclusions
  8. Spectra of Candidate Counterparts of GW231123

Figures (3)

  • Figure 1: The $90\%$ credible localization regions (left) and the luminosity distance posterior distributions (right) from different waveforms. The grey points in left panel mark the positions of AGNFCC flares whose peak times occur after the trigger of GW231123.
  • Figure 2: ZTF g-band photometry, r-band photometry, and g-r color for AGN flares that are selected as potential EM counterparts of GW231123.
  • Figure 3: The spectra for the AGNs potentially associated with GW231123.