The First Model-independent Upper Bound on Microlensing Signature of the Highest-mass Binary Black Hole Event GW231123
- 1Tata Institute of Fundamental Research, Homi Bhabha Road, Navy Nagar, Colaba, Mumbai 400005, India
Abstract
The recently discovered gravitational-wave event GW231123 is the most massive binary black hole merger detected to date. The inferred source masses of the event fall within the pair-instability supernova mass gap, where black holes formed directly from stellar progenitors are expected to be rare, making alternative formation scenarios for such massive black holes especially relevant. One proposed explanation is gravitational lensing, which can make the source masses to be inferred higher than their true values. In this work, we search for lensing signatures in GW231123, together with other O4a events, using a model-independent approach with μ- GLANCE . The method tests residual strain for correlated features across the detector network via cross-correlation and infers lensing-induced modulations within a Bayesian framework. Our analysis finds no strong evidence for lensing in GW231123 but reveals a potential residual feature that could be consistent with microlensing, with a modulation amplitude of up to 0.8 at 95% confidence. However, we find that waveform systematics for such heavy binary systems are sufficiently large to shadow the lensing signatures in short-duration signals like GW231123, preventing any definitive claim of lensing at this stage. We conclude that, if this event is lensed, similar lensed events will be detectable in the near future with current detector sensitivity, opening a new discovery space for lensed gravitational waves with the aid of more accurate waveform models.
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BibTeX
@article{chakraborty2026first,
title = {{The First Model-independent Upper Bound on Microlensing Signature of the Highest-mass Binary Black Hole Event GW231123}},
author = {Aniruddha Chakraborty and Suvodip Mukherjee},
journal = {The Astrophysical Journal},
year = {2026},
month = may,
doi = {10.3847/1538-4357/ae61a7},
url = {https://doi.org/10.3847/1538-4357/ae61a7},
note = {CC BY},
}
RIS
TY - JOUR
TI - The First Model-independent Upper Bound on Microlensing Signature of the Highest-mass Binary Black Hole Event GW231123
AU - Aniruddha Chakraborty
AU - Suvodip Mukherjee
PY - 2026
DA - 2026/05/11
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/ae61a7
UR - https://doi.org/10.3847/1538-4357/ae61a7
AB - The recently discovered gravitational-wave event GW231123 is the most massive binary black hole merger detected to date. The inferred source masses of the event fall within the pair-instability supernova mass gap, where black holes formed directly from stellar progenitors are expected to be rare, making alternative formation scenarios for such massive black holes especially relevant. One proposed explanation is gravitational lensing, which can make the source masses to be inferred higher than their true values. In this work, we search for lensing signatures in GW231123, together with other O4a events, using a model-independent approach with μ- GLANCE . The method tests residual strain for correlated features across the detector network via cross-correlation and infers lensing-induced modulations within a Bayesian framework. Our analysis finds no strong evidence for lensing in GW231123 but reveals a potential residual feature that could be consistent with microlensing, with a modulation amplitude of up to 0.8 at 95% confidence. However, we find that waveform systematics for such heavy binary systems are sufficiently large to shadow the lensing signatures in short-duration signals like GW231123, preventing any definitive claim of lensing at this stage. We conclude that, if this event is lensed, similar lensed events will be detectable in the near future with current detector sensitivity, opening a new discovery space for lensed gravitational waves with the aid of more accurate waveform models.
SN - 0004-637X
SN - 1538-4357
ER -