The anti-aligned spin of GW191109: glitch mitigation and its implications

TL;DR

This paper investigates how terrestrial detector glitches affect the inferred properties of GW191109, especially its anti-aligned spin, and explores different glitch models to assess the robustness of astrophysical interpretations.

Contribution

The study introduces joint inference methods for glitch and binary parameters, demonstrating how different glitch models influence the spin inference of GW191109.

Findings

Anti-aligned spin inference is robust under slow scattering noise models.

Flexible glitch modeling reveals a bimodal spin solution with a preference for anti-aligned spins.

Data alone cannot conclusively determine the true spin configuration due to glitch uncertainties.

Abstract

With a high total mass and an inferred effective spin anti-aligned with the orbital axis at the 99.9% level, GW191109 is one of the most promising candidates for a dynamical formation origin among gravitational wave events observed so far. However, the data containing GW191109 are afflicted with terrestrial noise transients, i.e., detector glitches, generated by the scattering of laser light in both LIGO detectors. We study the implications of the glitch(es) on the inferred properties and astrophysical interpretation of GW191109. Using time- and frequency-domain analysis methods, we isolate the critical data for spin inference to 35 - 40 Hz and 0.1 - 0.04 s before the merger in LIGO Livingston, directly coincident with the glitch. Using two models of glitch behavior, one tailored to slow scattered light and one more generic, we perform joint inference of the glitch and binary parameters. When the glitch is modeled as slow scattered light, the binary parameters favor anti-aligned spins, in agreement with existing interpretations. When more flexible glitch modeling based on sine-Gaussian wavelets is used instead, a bimodal aligned/anti-aligned solution emerges. The anti-aligned spin mode is correlated with a weaker inferred glitch and preferred by ~ 70 : 30 compared to the aligned spin mode and a stronger inferred glitch. We conclude that if we assume that the data are only impacted by slow scattering noise, then the anti-aligned spin inference is robust. However, the data alone cannot validate this assumption and resolve the anti-aligned spin and potentially dynamical formation history of GW191109.